Implements Forms, which are the basis for the Lazarus Graphical User Interface.

forms.pp contains classes, types, and routines used to implement forms, which are the basis for the graphical user interface in the Lazarus Component Library (LCL).

The following components are added to the Lazarus IDE component palette:

Standard Tab

TFrame

Additional Tab

TScrollBox
TApplicationProperties

The unit also includes the TApplication and TScreen classes used in the Application and Screen singletons.

Type used for a procedure that takes no arguments.

Used to define members in control classes.

Type used for an object procedure that takes no arguments.

Used to define members in control classes.

Represents the Position and Size of a Form on Screen.

TPosition is an enumerated type with values that describe the policy used to position and size a form instance in an application. TPosition is the type used to implement the Position property in TCustomForm. TPosition is used in the implementation of the MoveToDefaultPosition method in TCustomForm.

The Form appears exactly as it is positioned and sized in the Form Designer. The window manager decides how the form is to appear, in a default position and size. Keeps the designed form size, but position determined by window manager. Keeps the designed form position, but size determined by window manager. Centers the form on screen. Centers the form on the desktop (not recommended, use poScreenCenter). Centers the form on the Main Form. Centers the form on its Owner form. Represents the actual State of the window on the screen.

The actual meaning of each value depends on the platform:

Windows and Mac OS X: These operating systems support all values.
X11: The window state is a hint sent to the Window Manager, so more primitive Window Managers might ignore these hints.
Windows CE: In Windows CE platforms where Application.ApplicationType = atKeyPadDevice or atPDA (like in Windows Phone, PocketPC and Windows Mobile), wsMinimized and wsNormal are understood as wsMaximized, which is the normal state for windows in this platform. An exception are windows with BorderStyle=bsDialog or bsNone, which are allowed to have a custom position and size. For more information please read the Lazarus Wiki article.
Android: In this platform windows are always fullscreen.

Neither maximized nor minimized. The window is minimized and is not shown in the screen, but only in the taskbar. The window appears maximized. The exact behavior is up to the window manager, but usually the window appear occupying all of the work area of a monitor. The window appears in full screen mode, when allowed by the platform. It will, for example, attempt to appear on the top of task bars and other static platform user interface elements. wsFullScreen is converted to wsMaximized for use on the the Windows platform; the API does not provide a full screen option. What should happen when a form is closed. TCustomForm.OnClose Do nothing. The form is hidden. The form is destroyed. The form is minimized. Represents a standard action used to get a Hint value.

TCustomHintAction is a TCustomAction descendant. TCustomHintAction publishes the Hint property available in the ancestor. TCustomHintAction is the base class for THintAction defined in the StdActns unit.

TCustomHintAction is used in TApplication when setting the value for its Hint property and its OnHint event handler has not been assigned. TCustomHintAction is also used in the ExecuteAction method in TStatusBar when its AutoHint property is enabled.

TStatusBar.ExecuteAction THintAction The text used for the Hint. The orientation of a scroll bar. Horizontal scroll bar. Vertical scroll bar. The range for scroll bar increments. Scroll bar style flags. Default style; not used in the current LCL version. Scroll bar appears flat; Not used in the current LCL version. Scroll bar sends HotTrack messages; Not used in the current LCL version. Exception class raised in . Scroll bar type used in TScrollingWinControl.

Scrollable controls supply their own integrated scroll bars, one for horizontal and one for vertical scrolling. This class allows access to (one of) these integrated scroll bars.

A scrollable control has both a physical (visible) client size, and a logical (virtual) client size.

The Range property reflects the total virtual client size, in pixels.

The Page property corresponds to physical (visible) client size, in pixels, excluding the scroll bars. It also determines the size of the slider, relative to the total Range.

The Position property reflects the virtual origin of the visible client area, equivalent to the top coordinate of the slider. The Position can be changed by the user or by code.

Scroll bars usually appear only when Range is higher than Page, i.e. when the entire content cannot be shown at the same time. See the scroll bar properties in TScrollingWinControl for more details.

The virtual scroll range (Range - ClientSize), at least zero and never negative. The associated TScrollingWinControl instance. Gets the Handle for the associated TScrollingWinControl instance.

Provides the handle passed as an argument to routines in the LCL interface, including:

GetScrollInfo
SetScrollInfo
GetScrollbarSize
GetScrollbarVisible

GetScrollInfo SetScrollInfo GetScrollbarSize GetScrollbarVisible The handle for the associated control. The AutoScroll state for the associated TScrollingWinControl control. GetAutoScroll is not used as the read access specifier for the AutoScroll property. It is used in methods to ensure that the class reflects the current state for its associated control. True when the Control for the class instance has set its AutoScroll property. Gets the value for the Increment property. Value for the property. Gets the value for the Page property. Value for the property. Gets the value for the Position property. Value for the property. Gets the value for the Range property. Value for the property. Gets the value for the Size property. Value for the property. Gets the value for the Smooth property. Value for the property. True when the associated TScrollingWinControl and its handle are valid.

Used in methods which call LCL interface routines to avoid exceptions resulting from an unassigned control or an invalid handle value.

True when the associated TScrollingWinControl and its handle are valid. Implements the storage specifier for the Range property. True when AutoScroll is enabled for the scroll bar. Forces the associated control to update its scroll bars.

Calls the UpdateScrollBars method in the associated TScrollingWinControl instance when its handle has been allocated. No actions are performed in the method during LCL component streaming and when the component is freed.

Validates and applies the specified Range and updates the scroll bars.

Ensures that AValue is not less than zero (0). Applies the range limited value to the member for the Range property, and calls ControlUpdateScrollBars to refresh the scroll bars for the associated TScrollingWinControl instance.

InternalSetRange is called when the SetRange method updates the value for the Range property.

Value checked and applied to the Range property. Handler for scroll bar movement messages.

ScrollHandler is a method used to ensure that the control message in Message is applied to the Position property for the scroll bar. ScrollHandler uses the ScrollCode member from the TLMScroll instance to determine the actions needed in the method. It handles the following ScrollCode values:

SB_LINEUP: Decreases Position by the value in Increment.
SB_LINEDOWN: Increases Position by the value in Increment.
SB_PAGEUP: Decreases Position by the value in Page.
SB_PAGEDOWN: Increases Position by the value in Page.
SB_THUMBPOSITION: Sets Position to the value in the Pos member in Message.
SB_THUMBTRACK: Sets Position to the value in the Pos member in Message when Tracking is enabled. No actions are performed when Tracking is set to False.
SB_TOP: Sets Position to 0 (zero).
SB_BOTTOM: Sets Position to the value in the Range property.

No actions are performed in the method if Message has any other value in its ScrollCode member. No actions are performed in the method at design-time.

ScrollHandler ensures the the new value for the Position property is in the range 0..Range. Calls InvalidateScrollInfo to force scroll bar information to be re-initialized. Calls SetPosition to apply the new value for the Position property and scrolls the associated TScrollingWinControl accordingly. Sets the Result member in Message to 1 to indicate the control message was handled in the method.

ScrollHandler is called when the WMHScroll or WMVScroll methods in the associated TScrollingWinControl instance are used to handle scroll messages.

Control message examined in the method. New value for the property. New value for the property. New value for the property. New value for the property. New value for the property. New value for the property. New value for the property. New value for the property. Updates the state and position for the scroll bar in the associated Control.

UpdateScrollBar is a procedure used to update the state and position for the scroll bar in the associated Control.

When Control is a TScrollingWinControl instance, TScrollInfo is captured using the Range, Position, and Page properties. The scroll bar information is applied to the associated control by calling SetScrollInfo.

TScrollInfo values are not applied when a handle has not been allocated for the control, or when Control is not a TScrollingWinControl class instance.

UpdateScrollBar calls SetPosition to apply the current value in Position to a visible scroll bar in the class instance. When Control is a TScrollingWinControl instance, the Smooth property is used to determine if Increment needs to be adjusted to a value that is 10% of the Page size for the control.

UpdateScrollBar is used in the implementation of the ControlUpdateScrollBars method.

Renders scroll information invalid for the control.

InvalidateScrollInfo is used to mark the current TScrollInfo in the control as invalid. This occurs when a new value is assigned to the Position property, and when ScrollHandler applies position information found in TLMScroll messages. Calling InvalidateScrollInfo results in TScrollInfo being updated and applied for scrolling window controls in the UpdateScrollBar method.

TLMScroll Gets the horizontal scroll bar for the control. TControlScrollBar instance representing the scroll bar. Get the vertical scroll bar for the control. Scroll bar for the control, or Nil when not a TScrollingWinControl descendant. Determines whether a scroll bar is required. True when Visible, and Range is larger than the Page size. Constructor for the class instance.

Create is the constructor for the class instance, and calls the inherited constructor on entry.

Create sets the associated control for the class instance and the Kind property to the values specified in the AControl and AKind arguments. Create sets the default values for properties, including:

Page: Set to 80.
Increment: Set to 8.
Position and Range: Set to 0 (zero).
Smooth and Tracking: Set to False.
Visible: Set to True.

TObject.Create The windowed control in which the scroll bar is found. The scroll bar orientation. If Source is a TControlScrollBar, copies properties to itself, else performs inherited Assign.

Assigns the contents of the source object to the current object; in particular finds the Increment, Position, Range and whether smooth scrolling is to be feature and whether the scroll bar is visible.

TPersistent.Assign TControlScrollBar instance with the values copied in the method. Determines if the scroll bar is visible using the state from the widgetset class.

IsScrollBarVisible is a Boolean function used to determine if the scroll bar for the associated control is visible. The return value defaults to the value in the Visible property. If the handle has been allocated for the control, the GetScrollbarVisible routine from the LCL interface is used to get the visibility for the scroll bar Kind.

IsScrollBarVisible is used in the implementation of the ClientSizeWithBar and ClientSizeWithoutBar methods.

True if the scroll bar is visible. The Position for the scroll bar, or zero if not Visible. The scroll bar Position, or zero if not Visible. Gets the scroll bar with the opposite orientation (horz/vert) of the current instance. TControlScrollBar instance for the opposite orientation. The adjustable size of the scroll bar.

The length of the bar is the Width (or Height) of the Parent Control, the Size is the other (free) coordinate.

Returns the size for the associated control.

ControlSize is an Integer function used to get the size for the associated control in the class instance. Uses the value in Kind to determine the control property used as the return value. When Kind is sbVertical, the Width for the associated Control is used. When Kind is sbHorizontal, the Height for the associated Control is used.

Size for the associated control. Gets the size for the scroll bar based on the client area in the associated control.

ClientSize is an Integer function used to get the size from the client area in the associated control. ClientSize uses the value in Kind to determine whether the height or width for the associated control is used as the return value. For example:

sbVertical: Returns the client width from the associated control.
sbHorizontal: Returns the client height from the associated control.

ClientSize is used in methods like ClientSizeWithBar and ClientSizeWithoutBar to get the size for the scroll bar adjusted for scroll bar spacing returned from GetSystemMetrics.

Size from the client area in the associated control. Calculates the size of the associated control when the scroll bar is Visible.

ClientSizeWithBar is an Integer function used to calculate the client area for the associated control when the scroll bar is Visible. The return value contains the calculated value from ClientSize. If the scroll bar is not Visible, additional spacing (for the SM_SWSCROLLBARSPACING system metric) between the scroll bar and its associated control is removed from the return value.

ClientSizeWithBar is used in the implementation of the ComputeScrollbars method in TScrollingWinControl when the Range for the scroll bar would exceed the space available on the control, and in the GetPreferredSizeClientFrame method.

Size for the client area after adjusting for a visible scroll bar. Calculates the size of the associated control when the scroll bar is not Visible.

ClientSizeWithoutBar is an Integer function used to calculate the client area for the associated control when the scroll bar is Visible. The return value contains the calculated value from ClientSize. If the scroll bar is Visible, additional spacing (for the SM_SWSCROLLBARSPACING system metric) between the scroll bar and its associated control is added to the return value.

ClientSizeWithoutBar is used in the implementation of the ComputeScrollbars and GetPreferredSizeClientFrame methods in TScrollingWinControl.

Size for the client area when the scroll bar is hidden. The small Position increment, applicable to the scroll bar arrows.

Increment is a TScrollBarInc property which indicates the amount the client area in the associated control is scrolled when the Up or Down navigation arrows on the scroll bar are clicked. The default value is 8.

The value in Increment may be automatically recalculated in the UpdateScrollBar method when the Smooth property is enabled and the associated control is a TScrollingWinControl descendant. This is done to ensure that Increment contains 10% of the value for the Page property.

Increment is used in the ScrollHandler method when updating the Position property for scroll bar messages received in the control.

The orientation for the scroll bar: horizontal or vertical.

Kind is a read-only TScrollBarKind property which indicates the orientation for the scroll bar. The value for Kind is passed as an argument to the Create constructor, and stored in the property. The value in Kind is used in methods which update properties or state for the control, such as:

Position
Range
Page
Tracking
Size
ClientSize
ControlSize
IsScrollBarVisible
GetOtherScrollBar
UpdateScrollBar

The slider size, position increment applicable to the scroll bar area beneath the slider.

The amount by which the scroll indicator moves if the cursor selects the scroll bar above, below or on either side of the scroll indicator. The default value is 80.

Enables smooth scrolling, with automatic adjustment of Increment and Page.

Smooth is a Boolean property that indicates if the associated control is scrolled using an Increment value computed to be 10% of the Page size for the scroll bar. Set Smooth to True when the scroll bar should use a scrolling increment based on the size of the client area in the associated control. When Smooth is set to False, the Increment property determines the size for the scroll operation when the Up or Down arrows are clicked.

Smooth is used in the UpdateScrollBar method, and when set to True causes the value in Increment to be recalculated using the proportional size value. Smooth is relevant when the associated control is descended from TScrollingWinControl.

The default value for the property is False.

Position of the slider, 0..Range-Page.

The Position reflects the top coordinate of the slider, which is Range-Page when the slider is at the bottom of the bar.

The virtual size of the Parent Control. Gives feedback while the slider is dragged.

When it takes a significant amount of time to repaint the parent control at a new position, Tracking should be False to prevent flicker. This causes the control to be updated only when the slider is released.

Hides the scroll bar when False (default True).

The scroll bar widget is visible only if (Visible=True) and (Range>Page).

Set Visible to False to disallow the user to scroll the content, while the content still can be scrolled by code.

Use IsScrollBarVisible to get the current visible state of the widget.

Class of a windowed control with incorporated scroll bars.

This class introduces a logical (virtual) client area, part of which is visible in the physical (visible) client area. ScrollBars allow the user to scroll through the logical client area.

TScrollingWinControl is the ancestor for components like TScrollBox and TCustomDesignControl, and indirectly for TCustomFrame and TCustomForm.

Prevents recursive updates, True while an update is already in progress. Hides scroll bars with valid handles. Aligns the controls which have the class instance as their parent.

Calls the inherited method to align the specified control and its children to the parent control. Ensures that the page, range, and position in the scroll bars are recalculated when AutoScroll is enabled and both HorzScrollBar and VertScrollBar are in use.

TWinControl.AlignControls Control aligned in the method. Client rectangle used in the operation. Indicates if automatic scrolling is enabled for the control.

AutoScrollEnabled is a Boolean function which indicates if automatic scrolling is enabled for the control. The return value is True when the control is NOT automatically resized, or used as a dock site by an active docking manager.

Use the AutoSize property to enabled or disable automatic control resizing. Set the UseDockManager property to False to disable use of the DockSite for the control.

True when not automatically resized or used as a dock site. Sets or resets the ranges used for scroll bars in the control. Used in the implementation of the ComputeScrollbars method. Creates the window handle for the control.

Ensures that the scroll bar page, range, and visibility are established when the handles for the windowed control are created. Temporarily disables auto-sizing in the method, and re-enables auto-sizing prior to exit. Calls the inherited method to create the window and its handles.

TWinControl.CreateWnd The origin for the physical client area. TControl.GetClientScrollOffset The scroll bar Positions, or (0,0) if no scroll bars in use. Returns the full virtual ClientRect. TControl.GetLogicalClientRect TRect instance with the client rectangle adjusted for scroll bars visible on the control. Also updates scroll bars if needed. TControl.DoOnResize Calculates the size of the client area for the control excluding visible scroll bars. TControl.Height TControl.Width TControl.ClientHeight TControl.ClientWidth Width of the client area. Height of the client area. Performs actions needed to handle WMSize messages.

WMSize is a procedure used to perform actions needed to handle WMSize messages for the control. WMSize calls the inherited WMSize method to set the bounds for the control, optionally using the bounds from the parent control.

WMSize provides support for setting the window state based on size messages that originate in the LCL interface, and calls Resizing to realize the new window state.

Message examined in the method. Delegates scroll messages to the handler for the horizontal scroll bar. Message forwarded to the scroll bar. Delegates scroll messages to the handler for the vertical scroll bar. Message forwarded to the scroll bar. Updates Page, AutoRange, IsScrollBarVisible, and returns True when changed. True when something has been changed in the scroll bar settings. Sets the value for the AutoScroll property.

When the property is changed to True, the UpdateScrollBars method is called to calculate the page, range, and visibility for HorzScrollBar and VertScrollBar. When changed to False, the HideScrollbars method is called to reset the page, range, and visibility for the scroll bars. If the BoundsRect is updated in either method, the original value is restored prior to exit.

TScrollingWinControl.AutoScroll New value for the property. Performs actions when the component has been loaded from the LCL streaming mechanism.

Loaded is an overridden method in TScrollingWinControl, and calls the inherited method on entry. It calls UpdateScrollBars to compute the page, auto ranges, and visibility for the scroll bars when AutoScroll is enabled.

TWinControl.Loaded Performs actions needed when the control processes the WMSize message.

Resizing is an empty implementation in TScrollingWinControl. It must be implemented in a descendent class.

Window state for the windowed control. Indicates whether scroll bars are automatically displayed or hidden when needed.

AutoScroll is a Boolean property which indicates if scroll bars are automatically displayed or hidden on the control as needed. The default value for the property is False.

Changing the value for the property causes the Visible property in both HorzScrollBar and VertScrollBar to be updated (if needed). When set to True, the UpdateScrollBars method is called to calculate the page, range, and visibility for the scroll bars. When set to False, the HideScrollbars method is called to reset and hide the scroll bars (when assigned).

Sets the value for the AutoSize property. TControl.AutoSize New value for the property. Constructor for the class instance.

Create is the overridden constructor for the class instance, and calls the inherited method on entry. It allocates resources needed for the VertScrollBar and HorzScrollBar properties, sets the default value in AutoScroll to False, and sets the initial bounds for the class instance.

Owner of the class instance. Destructor for the class instance.

Destroy is the overridden destructor for the class instance. Destroy frees resources allocated for the HorzScrollBar and VertScrollBar properties. Destroy calls the inherited destructor prior to exiting from the method.

Initializes or updates the scroll bars for the control.

UpdateScrollbars is a method used to update the scroll bars used on the windowed control.

When automatic scrollbars are enabled using AutoScroll, the scroll bar information is initialized as needed for the visible scroll bars. The UpdateScrollBar method in both VertScrollBar and HorzScrollBar is called to recalculate the current page and range in the scroll bars.

No actions are performed in the method if a handle has not been allocated for the control, or when either HorzScrollBar or VertScrollBar has not been assigned.

Recursive calls to the method are also ignored.

Tells the widget to scroll the client area by the specified relative values.

ScrollBy calls the inherited ScrollBy_WS to apply the relative horizontal and vertical values to the widgetset class instance. An exception is raised if the handle has not been allocated. The still visible part doesn't deserve a repaint (optimization).

Horizontal distance for the scroll operation. Vertical distance for the scroll operation. Aligns the specified control to its parent and scrolls it into view.

ScrollInView is a method used to align and scroll the control in AControl into the visible area for the scrolling window control. No actions are performed in the method under the following conditions:

AControl has not been assigned (contains Nil).
The control is not the Parent (or ancestor) for AControl.
Neither horizontal nor vertical scroll bars are displayed for the control.

The origin for AControl relative to its Parent is determined by calling the ClientToParent method. OffsetRect is called to apply the offset to the display rectangle for AControl. The adjusted coordinates are used to reposition the visible scroll bars so that AControl is visible in the client area for the scrolling window control.

TControl.ClientToParent OffsetRect Control to make visible in the scrolling window control. The horizontal scroll bar for the control.

HorzScrollBar is a TControlScrollBar property with the horizontal scroll bar for the scrolling window control. The scroll bar is displayed for the control when its Visible property is True, or when Width is larger than the ClientWidth for the control and AutoScroll is enabled.

TControl.ClientWidth TControl.Width The vertical scroll bar for the control.

VertScrollBar is a TControlScrollBar property with the vertical scroll bar for the scrolling window control. The scroll bar is displayed for the control when its Visible property is True, or when Height is larger than the ClientHeight for the control and AutoScroll is enabled.

TControl.ClientHeight TControl.Height Implements a windowed control with scroll bars.

TScrollBox is a TScrollingWinControl descendant that implements a windowed control with scroll bars. TScrollBox sets the visibility for properties inherited from the ancestor class. TScrollBox includes an overridden constructor which sets the default values for properties in the class instance.

Constructor for the class instance.

Create is the overridden constructor for the class instance. It calls the inherited method on entry, an updates the component and control style flags as needed for the class instance. It sets the default values for the following properties:

AutoScroll (True)
BorderStyle (bsSingle)

TScrollingWinControl.Create Owner of the class instance. Indicates whether scroll bars are automatically displayed or hidden when needed.

AutoScroll is a Boolean property which indicates if scroll bars are automatically displayed or hidden on the control as needed. The default value for the property is True in TScrollBox.

Changing the value for the property causes the Visible property in both HorzScrollBar and VertScrollBar to be updated (if needed). When set to True, the UpdateScrollBars method is called to calculate the page, range, and visibility for the scroll bars. When set to False, the HideScrollbars method is called to reset and hide the scroll bars (when assigned).

TScrollingWinControl.AutoScroll TScrollingWinControl.UpdateScrollbars TScrollingWinControl.HorzScrollBar TScrollingWinControl.VertScrollBar Line style used to draw the border around the control.

The default value for the property is bsSingle in TScrollBox.

TWinControl.BorderStyle Indicates if the control uses the background from its Parent control.

ParentBackground is a Boolean property which indicates if the background for the Parent control is drawn as the background for the current control instance. The default value in TScrollBox is False.

ParentBackground is True when csParentBackground is included in the ControlStyle property. Setting the value in ParentBackground causes ControlStyle to be updated to include or exclude the csParentBackground enumeration value; it is included when True.

TWinControl.ParentBackground TControl.ControlStyle TControl.Parent TControlStyle TControlStyleType Provides a designer surface for scaling and layout of its child controls.

TCustomDesignControl is a TScrollingWinControl descendant which provides a designer surface used for scaling and layout of its child controls.

Properties are provided to set the display density (Pixels Per Inch) for design-time and run-time usage, and to Scale child controls. Methods are also provided to use TLayoutAdjustmentPolicy to layout and to re-size the child controls.

An overridden Loaded method is provided to adjust the design-time PPI (when scaling is enabled in the application).

TCustomDesignControl is used as the ancestor for TCustomFrame and TCustomForm.

Sets the value for the DesignTimePPI property. New value for the property. Sets the value for the Scaled property. New value for the property. Applies size and layout changes to the design surface and its Parent control.

DoAutoAdjustLayout is a procedure used to perform actions needed to apply size and layout changes to the design surface and its Parent control.

DoAutoAdjustLayout adjusts the height and width for the design surface by the specified scaling factors. Similarly, the BorderSpacing and Constraints in the control are adjusted using the scaling factors. Finally, the SetBounds method is called to apply the new values for Height and Width to the design surface.

No actions are performed in the method when the Parent property has not been assigned (contains Nil). In addition, no actions are performed when AMode omits the lapAutoAdjustWithoutHorizontalScrolling and lapAutoAdjustForDPI enumeration values. TControl.AutoAdjustLayout TControl.Constraints TControl.BorderSpacing TControl.Parent TLayoutAdjustmentPolicy TLayoutAdjustmentPolicy applied in the method. Horizontal scaling factor applied in the method. Vertical scaling factor applied in the method. Constructor for the class instance.

Create is the overridden constructor for the class instance. Create calls the inherited method using the value in TheOwner as the the owner of the class instance. Create sets the default values for the following properties:

Scaled
DesignTimePPI
PixelsPerInch

When scaling is enabled in the Application, the value in DesignTimePPI is used as the PixelsPerInch setting in the Font property.

TControl.Font Owner of the class instance. Applies a new display density (Pixels Per Inch) for a layout policy to the control.

AutoAdjustLayout is used to set the value in the PixelsPerInch property to the value specified in AToPPI for the lapAutoAdjustForDPI layout policy. AutoAdjustLayout calls the inherited method.

No additional actions are performed in the method when AMode contains a value other than lapAutoAdjustForDPI. Layout policy to use for the design surface. Original display density setting. New display density setting. Original form width. New form width. Design-time Pixels Per Inch for the designer surface.

DesignTimePPI is an Integer property that contains the display density (or Pixels Per Inch) used on the designer surface. The default value for the property is 96.

The property value is normally set when the component is loaded using the LCL streaming mechanism. It can be assigned at design-time to the value in ADesignTimePPI only when the new value matches the display density for the current Screen where the designer surface is used. The value can be changed at run-time, but the programmer must ensure that the value is valid for the intended usage.

An EInvalidOperation exception is raised if an invalid value is specified at design-time.

When scaling is enabled in the Application, the value in DesignTimePPI is assigned to the Font for the designer surface.

Use PixelsPerInch to access the run-time display density for the designer surface.

TControl.Font Run-time Pixels Per Inch for the designer surface. Indicates if the design surface is scaled to reflect changes in display density (Pixels Per Inch). The base type for TFrame.

TCustomFrame is a TCustomDesignControl descendant which implements the base class for TFrame. A Frame is a named container for related components. Groups of controls can be place on a frame, and re-used in your applications.

A Frame has behavior very similar to a Form. Their unique ability is that they can be embedded into forms or other frames in the designer. Like forms, they are stored in two separate files: the code is stored in a .pas unit file, and the design is stored in a .lfm file.

Frames can be created and designed in the Lazarus IDE by creating a new Frame module, and using the unit in your application. An existing frame can be added using the TFrame component on the Standard tab in the Lazarus IDE; you will be prompted for the TFrame class to use for the component.

Frames can also be created entirely in code at run-time. They do not have to be installed in the Lazarus IDE. One drawback is that complex inheritance hierarchies for TFrame classes can be problematic; they do not propagate changes to all derived frames in a multi-level inheritance tree.

Adds the specified list of Actions to the Parent form for the frame class. No actions are performed in the method when a Parent form has not been assigned for the class instance.

AddActionList is called from the Notification method when a TCustomActionList instance has been added to the control. This occurs when a new Parent is assigned for the frame instance.

TControl.Parent List of Actions added in the method. Removes the specified list of Actions from the Parent form. No actions are performed in the method when a Parent form has not been assigned for the class instance.

RemoveActionList is called from the Notification method when the TCustomActionList instance has been added to the control. This occurs when a new Parent which contains an action list is assigned for the frame instance.

TControl.Parent List of Actions removed in the method. Implements reading the Left property for the designer surface. Implements reading the Right property for the designer surface. Implements writing the Left property for the designer surface. Implements writing the Top property for the designer surface. Invokes Proc for all Controls and also for all Components without a Parent. TWinControl.GetChildren The callback method. Components are enumerated only if Root=Self. Adds or removes an action list for the control. TControl.Notification TComponent.Notification Component for the notification. Operation for the notification. Sets the value for the Color property.

SetColor is an overridden method in TCustomFrame used to set the value for the Color property. It calls the inherited method on entry.

When the value for the Color property is set to clDefault, or has the same value as the Color property in Parent, no additional actions are performed in the method. Otherwise, the value in ParentBackground is set to False.

TControl.Color New value for the property. Sets the value for the Parent property.

Updates the action list for child components or nested frames by calling AddActionList or RemoveActionList. Frees the Handle for the control when Parent has not already been assigned. Calls the inherited method to update the value in Parent. Performs automatic layout adjustments when the PixelsPerInch settings for the Parent and the frame instance have different value.

TControl.Parent TControl.SetParent New value for the Parent property. Sets the value for the ParentBackground property.

Ensures that Color is changed to the value in the Parent control when the property is set to True. Color is set to clDefault when the property is set to False. Calls UpdateOpaque to ensure that the csOpaque style flag is applied to the ControlStyle property as needed.

New value for the ParentBackground property. Handles the CM_PARENTCOLORCHANGED message for the control.

CMParentColorChanged is an overridden method in TCustomFrame. It calls the inherited method on entry to update the values in Color and ParentColor. If the control has finished loading using the LCL component streaming mechanism, the UpdateOpaque method is called to update flag values in the ControlStyle property. ControlStyle is not updated if csLoading is included in the ComponentState property.

TControl.CMParentColorChanged TControl.ParentColor TControl.Color TComponent.ComponentState Control message handled in the method. Defines non-published properties that are included in LCL component streaming.

DefineProperties is an overridden method used to include non-published properties in the values read and written during LCL component streaming. In TCustomFrame, design-time information for the Top and Left coordinates for the frame are included (when available) in the specified TFiler instance.

TControl.DefineProperties TFiler instance where property definitions are added. Gets the preferred height and width for the control used during auto-sizing.

CalculatePreferredSize is an overridden method in TCustomFrame. It ensures that the inherited method is not called when the frame is an un-parented component and visible on the form designer. This allows the dimensions to be freely resized on the design surface. Values in the PreferredWidth, PreferredHeight, and WithThemeSpace arguments are not modified at design-time.

If the frame has an Owner (parent form) at run-time, the inherited method is called to get the values used in the LCL auto-sizing algorithms.

TWinControl.CalculatePreferredSize Preferred width for the control. Preferred height for the control. True if additional space is reserved in the width or height for theme details. Updates control style flags to reflect the transparency for the frame.

UpdateOpaque is a method used to update ControlStyle flags to reflect the transparency for the frame. When ParentBackground is True, the value csOpaque is excluded from the ControlStyle property to allow the frame to be drawn with transparency. When set to False, csOpaque is included in ControlStyle.

UpdateOpaque is called when the value for the ParentBackground has been changed, and when the CM_PARENTCOLORCHANGED control message is handled for the frame.

TControl.ControlStyle Constructor for the class instance.

Create is the overridden constructor for the class instance. Create calls the inherited method using AOwner as the owner for the class instance. Create sets the ControlStyle property to the following enumeration values:

csAcceptsControls
csCaptureMouse
csClickEvents
csSetCaption
csDoubleClicks
csParentBackground

Create uses the default size for its class type to set the initial bounds for the control.

Raises an EResNotFound exception at run-time if the ClassType for the class instance is not derived from TFrame. TComponent.Create Owner of the class instance. Gets the default dimensions for a new instance of the class.

GetControlClassDefaultSize is an overridden method in TCustomFrame, and does not call the inherited method. The return value is a TSize instance with the width and height for the new class instance in its X and Y members. The default dimensions in TCustomFrame are 320 pixels wide (X member) by 240 pixels tall (Y member).

TSize type with the width and height for the new class instance. Indicates if the control uses the background from the parent.

The write access specifier is overridden in TCustomFrame. It calls the inherited method on entry.

If the new property value is True and ParentColor is True, the color assigned to the Parent control is stored in the Color property. Otherwise, Color is set to the value clDefault. The UpdateOpaque method is called to adjust the control style flags for the control.

The default value for the property is True.

TWinControl.ParentBackground TControl.Color TControl.Parent Class type used to create new instances of TCustomFrame. Frames can be designed like Forms and used like custom controls, without much coding or installation in the IDE.

TFrame is a TCustomFrame descendant which implements a named container for related components. Groups of controls can be place on a frame, and re-used in your applications.

TFrame contains a new property which indicates the LCL (Lazarus Component Library) version number used in the container. An overridden constructor is also introduced to initialize the value in the LCLVersion property. TFrame sets the visibility for properties defines in ancestor classes.

Constructor for the class instance.

Create is the overridden constructor for the class instance. It sets the value for the LCLVersion property to the lcl_version constant defined in the lclversion.pas unit. Create calls the inherited constructor prior to exiting from the method.

lcl_version Owner of the class instance. LCL version number for the frame instance.

The value in LCLVersion is assigned in the Create constructor using the lcl_version constant defined in the lclversion.pas unit. Its value is stored during LCL component streaming if a value has not been assigned to the Parent for the control.

TControl.Parent lcl_version Represents a visual element in a window title bar; depends on window manager support.

biSystemMenu: The form has a System menu (Maybe not all windowmanager supports this)
biMinimize: The form has an minimize button
biMaximize: The form has a maximize button
biHelp: When you click this button a Question Cursor appears, and the help routines are called if you click on an control

Window has a system menu. Window has an Minimize button. Window has an Maximize button. Window has an Help button. The preferred monitor for showing a form.

When a form is not assigned to a specific monitor, assume the following display context:

dmDesktop: No attempt to choose specific monitor
dmPrimary: On the primary monitor
dmMainForm: On the same monitor as the main form; if there is no main form then use dmPrimary behavior
dmActiveForm: On the same monitor as the currently active form; if there is no active form then use dmMainForm behavior

Place the form on the full desktop. Place the form on the primary monitor. Place the form on the same monitor as the main form. If there is no such form then use the primary monitor. Place the form on the same monitor as the currently active form. If there is no such form then use the primary monitor. Form state flags.

The form states are:

fsCreating: initializing (form streaming)
fsVisible: form should be shown
fsShowing: form handling WM_SHOWWINDOW message
fsModal: form is modal
fsCreatedMDIChild: not yet implemented
fsBorderStyleChanged: border style changed before window handle creation
fsFormStyleChanged: form style is changed before window handle creation
fsFirstShow: form is shown for the first time
fsDisableAutoSize: disable auto-size

initializing (form streaming). form should be shown. form handling WM_SHOWWINDOW message. form is modal. not yet implemented. border style changed before window handle creation. form style is changed before window handle creation. form is shown for the first time. disable auto-size. Set type used to store values from the TFormState enumeration.

TFormState is the type used to implement the FormState property in TCustomForm and descendent classes.

Dummy type for the values that can be returned as a modal result.

Even though the type is defined as an integer, only the defined constant values should be used (mrOK, mrCancel, et. al.).

TForm Notification handler types. Notified on first form Show. Notified on form Close. Notified after form Create. How a form is represented in the TaskBar. Uses the default rules from the platform for showing the form in the TaskBar. Always show the form in the TaskBar. Never show the form in the TaskBar. Defines the handling performed for a parent window in forms and dialogs.

TPopupMode is an enumerated type with values that specify how the parent is determined for a form or dialog. TPopupMode is the type used for the PopupMode property in TCustomForm.

modal: align to active form or main form; non-modal: no window parent.

For modal windows, the handle has to be recreated in ShowModal. If this is not wanted, please use explicitly pmAuto before calling ShowModal.

modal and non-modal: align to active form or main form. modal and non-modal: align to PopupParent or main form. Type used for an OnClose event handler in a form.

Closing a form can have several meanings:

caNone: Do nothing (don't close).
caHide: Hide the form (default for modal forms).
caFree: Destroy the form.
caMinimize: Minimize the form (MDI child default).

The handler can set CloseAction to the desired value for the action.

The form that received an Close request. Set this to caNone, to prevent the form from closing. Specifies an OnCloseQuery handler event handler.

TCloseQueryEvent is an object procedure type which specifies the event handler signalled to determine if a form can be closed.

TCloseQueryEvent is the type used to implement the OnCloseQuery property in TCustomForm. An application must implement an object procedure using the signature for the event handler to allow responding to the notification.

The form that received an Close request. Set to False to deny closing. Type used for an OnDropFiles event handler.

TDropFilesEvent is an object procedure which specifies an event handler triggered when files are dropped on a drag and drop-enabled control.

TDropFilesEvent is the type used to implement the OnDropFiles property in TCustomForm and TApplication. Applications must implement a procedure using the signature for the event handler, and assign it to the property.

The control that received the dropped files. The list of the dropped files. Type used for an OnHelp event handler.

THelpEvent is an object function which specifies an event handler signalled when Help is requested in an application or form. THelpEvent is the type used to implement the OnHelp event handler in TCustomForm and TApplication. Applications must implement a function using the signature for the event handler, and assign it to the property.

Indicates if the help request is satisfied by the event handler; False causes the default help handler for the application to be used. Help command type requested; either HELP_CONTEXT or HELP_COMMAND. Context data for the help request. False suppresses help display. Type used for an OnShortcut event handler.

A shortcut handler is invoked when a key is pressed, before any other processing. It can interpret the key as an shortcut and act accordingly. In this case, Handled should be set to True to prevent further processing of the key.

The key event message. Set Handled to True to prevent further processing of the key. Specifies an event handler signalled when a modal message dialog is completed.

TModalDialogFinished is an object procedure which specifies an event handler signalled when a modal message dialog is completed. The AResult argument contains the modal result constant returned from the message dialog.

TModalDialogFinished is the type used to implement the TCustomForm.OnShowModalFinished and TApplication.OnMessageDialogFinished properties.

TObject instance for the event notification. Modal result value from the dialog. The base type for TForm classes.

TCustomForm is a TCustomDesignControl descendant that implements the base type for TForm classes.

Forms represent a window or a dialog used as the user interface for a GUI application. It is a container where visual components (such as buttons, labels, edit fields, images, etc.) can be placed. It is also a designer surface which provides design-time support for configuration and layout of the content placed on the form.

TCustomForm acts an abstraction layer which masks implementation-specific routines required for the various widgetsets supported in the Lazarus Component Library (LCL). Methods and properties are provided which interact with the underlying Operating System or platform, and provide a common API for form-related operations.

Lists of installed Form notification handlers. Used to track Focus changes (Enter/Exit events). Tries to resolve stDefault in ShowInTaskBar using Application settings.

Calls ShowInTaskBar to get the visibility of an icon for the form.

When the return value is stDefault (or when called at design-time), the TaskBarBehavior property in Application is taken into consideration to get the actual return value. If the application displays a single button for the executable and its forms, the return value is set to stNever. If multiple buttons can be displayed in the task bar, the value stAlways is used. If the Application uses the value tbDefault, the value stDefault is retained in the return value.

Effect visibility for the form icon in the task bar. Gets the value for the Monitor property. Value for the property. Indicates whether Form properties should be stored in the stream.

IsForm is used as the storage specifier for selected properties in the class instance. Always returns True in TCustomForm.

True when the value for the various properties should be included in the LCL streaming mechanism. Closes a modal form.

CloseModal is a procedure which attempts to close a form that has been displayed by calling the ShowModal method.

CloseModal calls CloseQuery to determine the action performed in the method. When CloseQuery returns True, the close action is set to caHide and the OnClose event handler is signalled when assigned. Form handlers are notified of the close action.

When CloseQuery is False, the close action is used to determine how the request is handled. If the CloseAction is caNone, the value in ModalResult is set to 0 (zero). If the CloseAction is caFree, the Release method is called to allow the Application to free the form component.

If an exception occurs in the method, the value in ModalResult is set to 0 (zero) and the Application.HandleException method is called.

CloseModal does not forward the action to the widgetset class; that is performed in the ShowModal method to ensure it is executed in the widgetset class. Destroys the form icons. Loads the new form icons, and notifies the widgetset and all forms. Performs actions needed for delayed window move, resize, show, and activate messages.

DelayedEvent is a mechanism used to reduce the number of move, resize, show, and activate messages that occur for forms and their child controls.

DelayedEvent discards duplicate calls to the method; only the most recent message is processed. It is used in conjunction with the QueueAsyncCall method in TApplication. DelayedEvent decrements an internal counter used to track the number of pending delayed event messages. When the counter reaches zero (0), the message is applied.

When WindowState is changed to wsNormal, the window origin or size is restored. For delayed OnChangeBounds and OnChangeBounds messages, the DoOnShow and/or Activate methods are called when the form is Active. If the form has not already been displayed and activated, the DoOnResize or the DoOnChangeBounds method is called for the corresponding delayed message.

An integer pointer to the data for the event; not used in the current implementation. Remembers the last focused control. Called when the Focus changed.

SetWindowFocus is a procedure used to ensure that the active control in the form instance has the input focus when the forms receives focus. At run-time, the control in ActiveControl (when assigned) is used as the active control. At design-time, the active control is the design surface for the current form instance.

No actions are performed in the method when a handle has not been allocated for the active control, or the control cannot be focused.

SetWindowFocus calls the SetFocus routine in LCLIntf to change the focus to the handle for the active control, and when successful calls the Perform method in the control to post the CM_UIACTIVATE control message.

SetWindowFocus is used in the implementation of the SetFocus and SetActive methods.

Sets the value for the WindowState property.

SetWindowState sets the value for the WindowState property. Calls the ShowWindow routine at run-time when Showing is set to True.

New value for the property. Adds a form notification handler with the specified type and code.

AddHandler is a procedure used to add a form notification handler to the list of handlers in the form instance.

HandlerType is a TFormHandlerType enumeration value that defines the situation(s) where the form handler can be executed. See TFormHandlerType for more information about values in the enumeration.

Handler is a TMethod record with pointers to the code and optional data executed when the handler is invoked.

AsFirst indicates if the handler should be inserted as the initial handler in the method list (when True), or appended to the end of the list (when False).

AddHandler calls RaiseGDBException to raise an exception when the pointer to the Code in Handler has not been assigned.

AddHandler ensures that a TMethodList exists for handlers using the value in HandlerType, and calls the Add method in the TMethodList to store the Handler at the position needed for AsFirst.

AddHandler is called from the implementation of more specialized methods like AddHandlerClose, AddHandlerCreate, and AddHandlerFirstShow.

Raises a catchable exception if the Code property has not been assigned for the TMethod instance in Handler. Raised with the message 'TCustomForm.AddHandler'.

TMethodList TMethod Form handler type added in the method. Code to execute for the form handler. True if the new form handler is stored first in the list of handlers. Removes a form notification handler of the specified type. Handler routine removed in the method. Returns the first control in the form Tab order. Called when the main menu has been changed.

Ensures that handles for the Menu are valid for the form display style. The Menu is not displayed at run-time for a modal dialog form (BorderStyle is set to bsDialog); in this case, the DestroyHandle method in Menu is called to free the Handle for the Menu. (This is Delphi compatible).

The WindowHandle for the Menu is set to the Handle property from the form instance.

No actions are performed in the method if the Handle has not been allocated, or when Menu has not been assigned for the form.

Updates the widgetset class with the effective form visibility in the task bar.

Uses values in ShowInTaskBar and the TaskBarBehavior setting in Application to determine the effective visibility for the form in the task bar. Calls the SetShowInTaskbar method in the widgetset class to update the effective form visibility.

No actions are performed in the method for the following conditions:

When the form instance is the MainForm for the Application (it is handled by the application).
When the handle has not been allocated for the form instance.
When the form has a Parent control, or has been configured as a MDI Child form (FormStyle is fsMDIChild).
The form has not been made visible (Showing is False).

Handles the LM_ACTIVATE message which activates or deactivates the form.

Calls SetActive to update the value in the Active property to reflect the value for the Active member in Message.

When the form is being de-activated, the Deactivate method in Application is called. Otherwise, the Activate method in Application is called. The UpdateShowInTaskBar method is called ShowInTaskBar to determine the effective visibility for the form in the task bar.

Control message examined in the method. Handles the LM_CLOSEQUERY message used to close the window.

Calls the Close method to process and apply the ModalResult and CloseAction for the form. Sets the Result member in Message to 0 (zero) to indicate that WndProc should ignore the message; it has been handled in this method (and Close).

Control message examined in the method. Handles the LM_HELP window message for the form.

No actions are performed in the method at design-time, or when values have not been assigned to the HelpInfo member in Message.

When HelpInfo has a HELPINFO_WINDOW context type, FindControl is called to locate and display the help for the control with the item handle in Message. When HELPINFO_MENUITEM is the context type, GetHelpContext in Menu is called to locate the control ID in Message. If not found, the item handle in Message is used. As a default, the value in the Context property is used to display the context help.

Message examined in the method. Handles the LM_SHOWWINDOW window message for the form.

No actions are performed in the method when the form has already been made visible (FormState contains the value fsShowing).

Updates FormState to include the value fsShowing. Calls DoShowWindow to focus a control on the form (when needed). Removes fsShowing from FormState prior to exiting from the method.

Re-implements the method from the ancestor class; does not call the inherited method.

Message examined in the method. Handles the LM_SIZE window message for the form.

Re-implements the method from the ancestor class.

Ensures that auto-sizing is disabled for a size message for a top-level form (where Parent is not assigned) or from the LCL interface. This is done by including the value fsDisableAutoSize in the FormState property.

Calls the inherited method to apply the width, height, and window state values in Message.

Message examined in the method. Handles the LM_WINDOWPOSCHANGED window message for the form.

Re-implements the method from the ancestor class.

Ensures that auto-sizing is disabled for a position message to a top-level form (where Parent is not assigned), or from the LCL interface when new height or width values are provided. This is done by including the value fsDisableAutoSize in the FormState property.

Calls the inherited method prior to exit to apply the position and bounds for the form.

Message examined in the method. Handles the CM_BIDIMODECHANGED control message for the form.

Re-implements the method from the ancestor class. Calls the inherited method on entry using the value in Message to set the BiDiMode and adjust the size for the control.

Ensures that all components owned by the form are notified of the change to the BiDiMode property. This is needed for menus on the form. A TLMessage instance is constructed with the CM_PARENTBIDIMODECHANGED message and dispatched to all of the Components on the form not derived from TWinControl. TWinControl handles the notification for its descendants. Alignment is temporarily disabled during the process, and re-enabled prior to exiting from the method.

Control message examined in the method. Handles the CM_PARENTBIDIMODECHANGED control message for the form.

Sets the BidiMode property to the value in Parent when ParentBiDiMode is True and Parent has been assigned. When Parent has not been assigned, the BiDiMode property in Application is copied to the form instance.

Control message examined in the method. Handles the CM_APPSHOWBTNGLYPHCHANGED control message for the form.

Ensures that controls with a Glyph are notified when a change has occurred to a button glyph. Calls NotifyControls to broadcast Message to all Controls on the form.

Control message examined in the method. Handles the CM_APPSHOWMENUGLYPHCHANGED control message for the form.

Ensures that menus and menus items are notified of a change to a Glyph. Dispatches the value in Message to all Components on the form.

Control message examined in the method. Handles the CM_ICONCHANGED control message for the form.

Frees and re-creates handle(s) for icons used on the form, and notifies the widgetset class by calling its SetIcon method.

Control message for the notification. Handles the CM_RELEASE control message for the form.

Calls the Free method to destroy the form instance.

Control message for the notification. Handles the CM_ACTIVATE control message for the form.

Ensures that the Menu for the MainForm in the Application is merged into the Menu for the form instance when FormStyle is fsMDIChild. This action is not performed at design-time, or when the MainForm or the Menu for the Application has not been assigned.

Calls Activate to signal the OnActivate event handler (when assigned) if needed.

Control message for the notification. Handles the CM_DEACTIVATE control message for the form.

This message occurs when the form loses focus within the application.

Calls the Deactivate method to signal the OnDeactivate event handler (when assigned). Ensures that the Menu merged to the application MainForm during activation is removed from the Menu for the Application. This action is not performed at design-time, or when Menu has not been assigned. It applies to a form using the fsMDIChild form style in an application using the fsMDIForm style in its MainForm.

Control message processed in the method. Handles the CM_SHOWINGCHANGED control message for the form.

Uses the value in Showing to determine whether the DoShow or the DoHide method is called. When Showing is True, the DoShow method is called to signal the OnShow event handler (when assigned) if needed. When Showing is False, the DoHide method is called to signal the OnHide event handler (when assigned).

If either event handler raises an Exception, it is ignored when HandleShowHideException is set to True. It is re-raised when HandleShowHideException is False.

Calls the inherited method prior to exit to notify the widgetset class of the window state change, and to update window control flags for the form.

Control message processed in the method. Handles the LM_DPICHANGED window message for the form.

Calls AutoAdjustLayout to apply the DPI setting in Message. This action is performed when:

The Parent for the form has not been assigned.
Scaled is enabled for both the Application and the form instance.
The DPI setting in Message is different than the PixelsPerInch value for the form.

Problem (Windows): if the form is shown the first time on a secondary monitor with a different DPI settings, the WM_DPICHANGED message is sent within UpdateBounds when BoundsLockCount>0 which means the bounds are not scaled. We force to update the bounds. See issue 32162. (A better solution is welcome.) Window message handled in the method. Member used to store the action lists associated with the form. Chooses the active control when the form becomes visible at run-time.

Calls a private method to locate the first visible and enabled control in the tab order for the form. Sets the value in ActiveControl to the control instance located in the method.

No actions are performed in the method at design-time, when ActiveControl has already been assigned, or when the form instance has a Parent.

DoShowWindow is called from the WMShowWindow method where the LM_SHOWWINDOW window message is handled for the form.

Notifies the OnActivate event handler.

Activate is a procedure used to signal the OnActivate event handler (if assigned) when the form is activated. Activate is called when the CM_Activate message is handled for the form.

Activate uses an internal member to determine whether the form is being displayed for the first time, or following a change of focus between forms. No actions are performed in the method when the form is being displayed for the first time and the WindowState property contains wsMaximized or wsFullScreen.

Use OnShow to respond to the event notification performed when the form is displayed for the first time.

Use OnChangeBounds or OnResize to respond to delayed changes to the form bounds (position) or resize events.

TControl.OnChangeBounds An empty implementation in TCustomForm. Can be implemented in a descendant to perform actions needed when the active form is changed. Just like Delphi VCL. Excludes borders from the given rectangle.

AdjustClientRect is an overridden method in TCustomForm which re-implements the method from the ancestor class. It is used to decrease the width and height for the client rectangle specified in Rect by the number of pixels in the BorderWidth property. It is used in the AlignControls method, and when auto-sizing is performed for Controls.

TWinControl.AdjustClientRect Client rectangle adjusted in the method. Increments the form update counter, and disables auto-sizing on the initial update lock.

Used with the EndFormUpdate method to manage auto-sizing during form updates. For the initial call to BeginFormUpdate, DisableAutoSizing is called to suspend auto-sizing.

Use EndFormUpdate to decrement the update counter. When the update count reaches 0, auto-sizing is re-enabled.

TControl.DisableAutoSizing TControl.EnableAutoSizing Implements the storage specifier for the Color property. TControl.Color True when Color has value other than clDefault or clBtnFace. Initializes parameters used to create the handle for the form instance.

CreateParams is used to initialize parameters needed to create the handle for the form instance.

CreateParams is an overridden procedure in TCustomForm, and calls the inherited method on entry. CreateParams ensures that values in the Params argument are valid. This includes setting the realized parent form and window handle for a form which is not the main form in the application. Style flags are also updated to indicate how the form is displayed in the task bar.

TWinControl.CreateParams Values examined and updated in the method. Creates the handle for the widgetset class and updates it Menu and Icons.

CreateWnd is an overridden method in TCustomForm used to create (or re-create) the Handle for the widgetset class. It sets the initial values for FormState, and calls the inherited method to handle auto-sizing and scroll bars.

CreateWnd ensures that a handle is allocated for the Menu and the Handle for the form is used as its WindowHandle. The CM_ICONCHANGED control message is performed to (re-)create handles for menu glyphs, and to post the changes to the widgetset class.

TScrollingWinControl.CreateWnd TWinControl.CreateWnd Performs actions when the form loses focus.

Called when the form loses focus in the application. Signals the OnDeactivate event handler (when assigned). Called from the CMDeactivate and WndProc methods.

Notifies handlers of the close action for the form.

DoClose is a method used to notify close handlers for the form instance of the action requested in the CloseAction parameter.

It is called from the Close method for a form that is not displayed as a modal dialog; i. e. FormState does not contain fsModal. It occurs after CloseQuery (and OnCloseQuery) have been called to determine if the form can in fact be closed, and the CloseAction has been set for the form style.

DoClose signals the OnClose event handler (when assigned) to allow the form instance to modify the CloseAction argument. It iterates over the close handlers in the form instance, and signals each of the TCloseEvent instances in the method list using CloseAction as an argument.

Close action to perform for the from instance. Notifies the create handlers for the form instance.

DoCreate is a method used to signal the create handlers for the form instance. DoCreate signals the OnCreate event handler (when assigned) to perform any actions needed for the new form instance. DoCreate also signals other create handlers to perform the methods using the current form instance as an argument.

If an Exception occurs in one of the event handlers, it is handled in the method when HandleCreateException returns True. When it returns False, the exception is re-raised in the method.

DoCreate calls LockRealizeBounds on entry to disable sending bounds changes to the widgetset class. UnlockRealizeBounds is called prior to exit to re-enable sending bounds changes to the widgetset class.

DoCreate is a called from the AfterConstruction method after the initial bounds for the form have been set, and before scaling and automatic layout adjustment are performed (if needed) for the new form instance.

TWinControl.LockRealizeBounds TWinControl.UnlockRealizeBounds Signals the OnDestroy event handler for the form instance.

DoDestroy is a method used to signal the OnDestroy event handlers assigned for the form instance. If an Exception occurs in the event handler, it is handled in the method when HandleDestroyException is set to True. When set to False, the exception is re-raised in the method.

DoDestroy is called from the BeforeDestruction method, and allows the application to perform actions needed before the form instance is physically freed. It is called after the form has been removed from the focus list for the Screen, hidden by calling the Hide method, and merged menu items have been removed from the MainForm for the Application.

Signals the OnHide event handler for the form instance.

Called from the CMShowingChanged method when Showing is set to False.

Signals the OnShow event handler when needed.

No actions are performed in the method when a maximized or full-screen window (WindowState contains wsMaximized or wsFullScreen) is displayed for the first time. It signals the OnShow event handler (when assigned) to perform the event notification.

DoShow is called from the DelayedEvent method in response to queued OnResize or OnChangeBounds events, and from the CMShowingChanged method when Showing is set to True.

TWinControl.Showing TControl.Parent Unlocks form updates; used with BeginFormUpdate. When the update counter reaches zero, FormEndUpdated is invoked to realize the pending changes. TWinControl.FormEndUpdated Indicates if an exception in the OnCreate event handler is handled by the application.

HandleCreateException is a Boolean function which indicates if an exception raised in the OnCreate event handler is handled in the form instance. The return value is True when the Application.CaptureExceptions property is set to True; the HandleException method in Application is called to notify its exception handlers of the exception. When the return value is False, the exception is re-raised in the caller.

HandleCreateException is called from the DoCreate method.

True when the exception is handled by the application. Placeholder for exception handlers in derived classes. By default the Application exception handler is invoked. True when the exception was handled. Placeholder for exception handlers in derived classes. By default the Application exception handler is invoked. True when the exception was handled. Initializes the widget, also for AlphaBlend and AllowDropFiles. TWinControl.InitializeWnd Performs actions when the component has been loaded using the LCL streaming mechanism.

Loaded is an overridden method in TCustomForm.

It disables alignment in the form, and adjusts the PixelsPerInch setting for the Font when it differs from the design-time setting. It is performed when Scaled is enabled for the form and the Application. This action is also performed for any child Controls. Calls the inherited Loaded method, and re-enables alignment for the form instance.

Ensures that the ActiveControl (when assigned) can receive focus. ActiveControl is set to Nil if the control cannot be focused for the form instance. Sets the Visible property to True when FormState contains the value fsVisible.

TComponent Called when handles for child control are created in the form instance.

ChildHandlesCreated is called after all handles for child controls are created. When this is a top-level form (Parent is Nil), the ParentFormHandleInitialized method is also called.

TWinControl.ChildHandlesCreated Handles the notification when a component is added to or removed from the form.

Notification is an overridden method in TCustomForm used to handle the notification when the component in AComponent has been added to or removed from the form instance. Operation is the action performed for the component.

Notification calls the inherited method on entry, and performs additional actions for the ActionList, Menu, and pop-up parent form used in the control.

TControl.Notification Component for the notification. Operation performed for the component. Calls the Paint method using the specified device context in the control Canvas.

PaintWindow is an overridden method in TCustomForm. It re-implements the method from the ancestor class, and does not call the inherited method.

PaintWindow assigns the device context in dc to the Canvas handle. The Paint method is called to signal the OnPaint event handler (when assigned). If a design surface is active for the form instance, its PaintGrid method is called. The Canvas handle is reset to 0 prior to exiting from the method.

TCustomControl.PaintWindow Device context (Handle) assigned to the Canvas for the form. Calls the user Alignment handler (AlignControls). Here: NOP for a top-level form. TControl.RequestAlign Performs actions needed when the form processes the WMSize message.

Uses the value in State to determine the action required in the method. The LCL interface is used to determine if the window state is valid for the widgetset. When allowed, the following methods are called for the corresponding TWindowState value:

wsMinimized: Calls the Minimize method in Application, or Restore if the Form is already minimized

If the value in WindowState has been changed, the method honors the value in the Position property if it was set to maximized at design-time. When the OnWindowStateChange event handler has been assigned for the form, it is signalled for the current class instance.

Window state applied in the method. Here: clip width and height of a top-level form to the monitor WorkArea. Performs a delayed resize action using the DelayedEvent for the control. Performs a delayed bounds change using the DelayedEvent for the control. Moves a top-level form in front or back of all forms. True for BringToFront. Sets the value for the Parent property.

SetParent is an overridden method in TCustomForm used to set the value for the Parent property.

SetParent disables auto-sizing before updating the property value. The Handle for the form is destroyed and re-created when Parent is both assigned and Visible.

SetParent ensures that the PixelsPerInch settings for the form instance and its Parent are the same. AutoAdjustLayout is called when the values differ and Scaled has been enabled for both the Parent form and the Application.

SetParent re-enables auto-sizing prior to exiting from the method.

TControl.Parent TControl.SetParent New value for the property. Moves the form to the location specified in the Position property.

MoveToDefaultPosition is a method used to move a form instance to the location specified in its Position property. It ensures that the form appears on the correct monitor for the values in the DefaultMonitor and Position properties.

DefaultMonitor is used to determine whether the form needs to be moved to a different monitor for the value in Position. For instance:

dmDesktop: The form does not need to be moved, and the current monitor is used.
dmPrimary: The PrimaryMonitor in Screen is used to display the form.
dmMainForm: If the Application has a MainForm, the monitor for the main form is used. Otherwise, the form is not relocated to another monitor.
dmActiveForm: If the Screen has an ActiveForm, the monitor for the active form is used. Otherwise, the form is not moved to another monitor.

Position specifies an associated form and the relative position for the relocated form instance. For instance:

poOwnerFormCenter: Uses the Owner form to center align the relocated form instance. If the Owner is not a TCustomForm instance, Position is converted to poMainFormCenter to center the form to the MainForm in the application.
poMainFormCenter: Centers the form to the MainForm for the Application. When not assigned, Position is converted to poScreenCenter to center the form on the Screen.
poScreenCenter: Centers the form on the default monitor.
poDesktopCenter: Centers the form to the desktop (width for all screens).
poWorkAreaCenter: Centers the form on work area for the default monitor.
poDesigned, poDefaultSizeOnly: Ignored in the method.
poDefault, poDefaultPosOnly: Uses the size / relative position provided by the widgetset class instance.

MoveToDefaultPosition gets the display rectangle for the form instance, and translates the form coordinates to the correct Monitor. SetBounds is called to apply the translated origin using the height and width for the form instance.

No actions are performed in the method when either Parent or the ParentWindow handle has been assigned for the form instance. No actions are performed in the method when WindowState contains wsFullScreen or wsMaximized.

MoveToDefaultPosition is called from the AllAutoSized, SetRestoredBounds, and UpdateShowing methods. It is also called when a new value is assigned to the Position property.

The implementation for the method was changed in LCL version 2.3.0. Configures and position the form when its visibility has been changed.

UpdateShowing is an overridden method used to configure and position the form instance when the visibility for the form has been changed.

When Visible is set to True at run-time, the MoveToDefaultPosition method is called to move the form to the monitor / location in the Position property. This action is not needed (or allowed) at design-time. When FormState indicates it is the first time the form is being displayed, the DoFirstShow method is called to notify event handlers for the form.

UpdateShowing calls the inherited method to update the Handle for the form and the visibility for any child Controls.

If ActiveControl is not assigned, and there is no Parent form, the FindDefaultForActiveControl method is called to locate the first visible and enabled child control on the form. Its Handle is used to focus the control using the LCL SetFocus routine.

Finally, the visibility of the form in the task bar is updated and passed to the widgetset class.

TWinControl.UpdateShowing Sets the value for the Visible property.

SetVisible is an overridden method used to set the value for the Visible property. It ensures that FormState is updated to reflect the new value for the property. When set to True, fsVisible is included in the FormState property. Otherwise, fsVisible is excluded from FormState. No actions are performed in the method if FormState already already reflects the new value for the property.

SetVisible calls the inherited method to store the new property value, and to perform resizing and control messages as needed. The UpdateVisible method in Application is called to ensure that the application is visible in the task bar when one of its forms is visible.

TControl.SetVisible New value for the property. If the the form is about to show, calculate its metrics.

AllAutoSized is an overridden method used to apply the position and layout for a visible form that about to be displayed. AllAutoSized implements the virtual method defined in the ancestor class.

AllAutoSized is called from the DoAllAutoSize method when AutoSize has been enabled, and occurs after the bounds for the form have been calculated. It calls the MoveToDefaultPosition method to move the form to the monitor and relative location in Position.

No actions are performed in the method if the form is already Showing or it is not Visible.

TWinControl.Showing TWinControl.AllAutoSized TWinControl.DoAllAutoSize Executes handlers using the FirstShow handler type.

Calls CallNotifyEvents in the internal method list for any methods using the fhtFirstShow handler type. The form instance is passed as an argument to the handler(s).

Called from the UpdateShowing method when the form is Visible and its Showing property is changed to True. Occurs after MoveToDefaultPosition has been to called to position the form on its monitor, and after the value fsFirstShow has been included in the FormState property.

TWinControl.Showing UpdateWindowState is an empty implementation in TCustomForm.

Has an empty implementation in the current LCL version.

Notifies all VisibleChanging handlers.

Calls the inherited method prior to exit. Called prior to setting the new value for the Visible property in a control (or form) in the SetVisible method.

TControl.VisibleChanging Notifies all handlers when the visibility for the form has been changed.

Calls the inherited method on entry.

When the Screen singleton has been assigned, its NotifyScreenFormHandler method is called to signal all snFormVisibleChanged handlers in the class instance.

Called after a new value has been assigned to the Visible property for the control (or form).

Handled messages include: Activate, SetFocus, KillFocus, Exit, Enter, Window Position Changing, and DrawItem.

WndProc is an overridden method which implements the processing loop for window and control messages received for the form instance. It extends the method from the ancestor class to provide form-specific support for messages including:

LM_SETFOCUS: Chooses the active control for the form at run-time, and ensures that the control is focused.
CM_EXIT: Deactivates a HostDockSite (when assigned) when the form loses focus.
CM_ENTER: Activates a HostDockSite (when assigned) when the form receives focus.
LM_WINDOWPOSCHANGING: Suppresses move or resize window messages as needed for the Position or BorderStyle properties.
LM_DRAWITEM: Handles owner-drawn Menu items for the item and command in the message.

WndProc calls the inherited method to handle control-specific messages not handled in the method.

Implements the storage specifier for the Visible property.

Returns the value in the Visible property.

True when the Visible property is set to True. Sets the value for the AutoSize property.

SetAutoSize is an overridden method in TCustomForm used to set the value for the AutoSize property.

When set to True, it updates FormState to exclude the value fsDisableAutoSize, and modifies Position to use poDefault when it contains poDefaultPosOnly.

TControl.AutoSize New value for the property. Sets the value for the AutoScroll property.

SetAutoScroll is an overridden method in TCustomForm used to set the value for the AutoScroll property. It calls the inherited method to apply the new property value, but includes an additional test for the BorderStyle used on the form. AutoScroll cannot be set to True when BorderStyle has a value other than bsSizeable or bsSizeToolWin.

New value for the property. Sets the value for the Scaled property.

SetScaled is an overridden method in TCustomForm used to set the value for the Scaled property. It calls the inherited method on entry. At run-time, the AutoScale method is called when the new property value is set to True and differs from the existing property value.

New value for the property. Adds the specified list of actions to the ActionList for the form.

Ensures that the TList instance is allocated for the internal member. Calls the IndexOf method in the list to locate the value in the List argument. If it is not found, the Add method for the list is called to append the value.

DoAddActionList is called from the Notification method when a TCustomActionList instance is added to the form (during LCL streaming).

List with actions added to the form instance. Removes the specified list of actions from the internal list.

Calls the Remove method in the TList member to delete the TCustomActionList specified in List.

DoRemoveActionList is called from the Notification method when a TCustomActionList instance is removed from the form.

TCustomActionList TCustomActionList instance removed in the method. Loads resources needed for the form. Calls InitResourceComponent to load resources for the current form instance. Raises an EResNotFound exception if RequireDerivedFormResource is set for the application, and a resource is not found for the form. Re-implements the auto-drag behavior for forms.

BeginAutoDrag is an overridden method in TCustomForm which re-implements the auto-drag and dock behavior for form instances. It allows form dragging only if it is docked (HostDockSite is assigned) to a site where a DockManager is not used (UseDockManager is False). It does not call the inherited method.

TControl.HostDockSite TWinControl.UseDockManager Docks or undocks the form in the specified dock site.

DoDock is an overridden method used to dock / undock the form instance in the dock site specified in NewDockSite. When NewDockSite is unassigned (contains Nil), the form instance is undocked from the host dock site.

ARect contains the bounds for the new dock site after resizing and alignment (when needed).

When a form is docked, its BorderStyle is set to bsNone. DoDock ensures that the value in the BorderStyle property is saved or restored for the form when the value in HostDockSite is changed. If NewDockSite has been assigned, the value in BorderStyle is saved to an internal member. If NewDockSite is Nil, the value in BorderStyle is restored from the internal member.

Changes needed for the Align property must be handled in the DockManager.

DoDock calls the inherited method prior to exit.

DoDock is called from the Dock method in an ancestor class.

TControl.Dock TControl.DoDock TControl.HostDockSite New dock site for the form instance. Rectangle with the bounds for the new dock site after resizing and alignment. Gets the value for the Floating properties. TControl.Floating TControl.GetFloating Value for the property. Default caption displayed when the form is docked.

GetDefaultDockCaption is an overridden String function used to get the default caption displayed when the form is docked. GetDefaultDockCaption returns the value in the Caption property.

Called from the GetDockCaption method in an ancestor class. The value is passed as an argument to the OnGetDockCaption event handler.

TWinControl.GetDockCaption TWinControl.OnGetDockCaption Default caption displayed when the form is docked. Handles the CM_ACTIONEXECUTE control message.

Calls DoExecuteAction to execute the TBasicAction passed as an argument in Message. Sets the Result member in Message to 1 to indicate that the action was performed in the method.

Called when a CM_ACTIONEXECUTE control message dispatched in the WndProc method in TApplication is processed for the form instance.

Control message examined in the method. Handles the CM_ACTIONUPDATE control message. Control message examined in the method. Asks all applicable components to execute an action.

First, the ActiveControl and the Form itself are asked to execute the action. Then, all child components are tried. The search stops as soon as the action is handled.

True when the action was handled. Action to execute. Tries all applicable components to update an action. DoExecuteAction True when the action was updated. Asks all components on the form to update their actions.

UpdateActions is a procedure used to update actions assigned to components on the form instance. No actions are performed in the method at design-time, or when the Showing property is set to False in the form instance.

UpdateActions applies updates for an assigned Menu in the form instance. Items on the Menu update their actions when the menu item is visible. Finally, all controls on the form instance are recursively searched; controls which are action clients update their actions when they are visible.

Update actions is called for each of the custom forms when the application enters an idle state, and occurs after processing queued asynchronous calls and the OnIdle event handler in the application.

TWinControl.Showing TControl.InitiateAction The Handle of the MDIForm client (container for MDI children). Constructor for the class instance.

Create is the overridden constructor for the class instance. Create sets the default values for internal members used in the form instance, and calls the CreateNew method to configure the visible aspects of the form instance. At run-time, it also calls ProcessResource to load the form content from its resource file.

Owner for the class instance. Creates a form instance without a resource (.lfm) file.

CreateNew is an alternate constructor for the class instance. CreateNew is used to create a new TCustomForm instance which is not loaded from a resource file (.lfm). It performs actions to initialize properties for the form instance, including:

Sets the FormState to fsFirstShow and calls BeginFormUpdate.
Sets the default BorderIcons for the form.
Sets the FormStyle, ControlsStyle, and BorderStyle for the form.
Calls the inherited Create constructor.
Sets the default bounds for the form instance.
Sets Visible to False.
Sets WindowState to wsNormal.
Allocates resources for the Icon property but does not assign a bitmap.
Sets the default value for Color.
Calls Screen.AddForm to register the form instance on the current screen.

Owner for the new class instance. Ignored in the current implementation. Destructor for the class instance.

Destroy is the overridden destructor for the class instance.

Destroy ensures that unhandled queued asynchronous calls in the Application instance are removed for the form.

Destroy disables auto-sizing to prevent resize messages while the form is being freed. Destroy frees resources allocated for the form instance, including its Icon and any allocated icon handles. The form instance is removed from Screen, and its ActionLists are freed. Destroy frees all form handlers added to the class instance.

Destroy calls the inherited destructor prior to exiting from the method.

Performs actions when the form has been created and loaded from its resource file.

Implements the virtual method defined in the ancestor class.

Called after the form instance has been created and loaded from its resource file (when needed).

Ensures that the initial bounds for the form are set to the values in the Left, Top, Bottom, and Right properties. Calls DoCreate to signal the OnCreate event handler (when assigned). Ends the form update started in the CreateNew constructor. Ensures that scaling and automatic layout are applied to form instance (if needed) when Scaled is enabled for both the form instance and the Application.

TObject.AfterConstruction Performs actions before the form instance is physically freed.

Calls the inherited method on entry to signal any OnBeforeDestruction event handlers assigned to the form instance.

Removes the form instance from the list of focused forms in the Screen singleton. At run-time, the Hide method is called when the form is not a MDI child form in the application. If the form is a MDI child form, merged menu items are removed from the menu in the MainForm for the Application.

TControl.BeforeDestruction Handle for the large icon used on the form. Closes the form.

Close does not necessarily destroy the form. Modal forms only are hidden. When the MainForm is closed, the application terminates.

An OnCloseQuery handler can refuse to allow the form to close.

Asks the OnCloseQuery handler whether the form can be closed. Updates ActiveControl if it is to be de-focused. The control which will lose focus. True if the control is no longer the ActiveControl. Ensures that the form is fully visible, and optionally brings it in front of all other forms. Bring the form to front if True. Gives focus to the specified control.

FocusControl is a procedure used to give focus to the control specified in WinControl. FocusControl ensures that the ActiveControl property is updated when needed, and may raise an exception if WinControl cannot be focused. If the form instance was not already Active, the SetFocus method is called.

If the control or one of its parents is not visible or disabled, an exception will be raised (in SetFocus). The control receiving the focus. Indicates if the BeginFormUpdate method has been called without a corresponding EndFormUpdate method call.

The method is used in TControl descendants to determine if the parent form for the control is already rendering changes to its content.

TControl.FormIsUpdating Returns True when the internal update counter for the form contains a positive non-zero value. Makes a Bitmap image with the Form content.

GetFormImage is a TBitmap function used to get a bitmap image with the contents for the form instance. The return value must be managed by the caller to ensure that the image is freed.

GetFormImage sets the size for the TBitmap instance to the values in the ClientWidth and ClientHeight properties. The GetWindowRect routine in lclintf is called to get the display rectangle for the form Handle. The PaintTo method is called to draw the rectangle to the Canvas in the bitmap.

The return value can be Nil if an Exception was raised and handled in the method.

Bitmap created in the method with the image for the form. The role(s) for the control in a modal form (default or cancel button). Gets the form that is the effective parent for the pop-up, dialog, or splash screen. Form instance that is the parent for the pop-up form, or Nil for a splash screen. Invokes the OnDropFiles handler of the form. This function is called by the LCL interface.

The drop files event will be invoked when the user drops one or more dragged files onto one of forms in the application. First this event should be fired for the target form (or main form if drop target is unknown), and then for the application instance.

Show help for control or menu item. This function is called by the LCL interface. TControl.ShowHelp Determines whether the specified message contains a shortcut or accelerator key.

Checks form components to determine whether the specified message is a shortcut or accelerator key used on the form. This includes signalling the OnShortcut event handler (when assigned), calling IsShortCut for the form Menu, or calling IsShortcut for the ActionLists for the form instance.

Returns True when the specified Message is an active as a shortcut.

True when the specified Key was handled as a shortcut. Control message examined in the method. Resizes the form for the specified monitor.

MakeFullyVisible is a method used to make the form instance fully visible on the specified monitor. It ensures the form fits within the required bounds for the monitor or work area. If the form is too wide or too tall, the form bounds are adjusted so that the form fits within the required bounds. This prevents the form from being partially visible on multiple monitors.

AMonitor is the TMonitor instance where the form is displayed. If AMonitor is not specified (contains Nil), the value in the Monitor property is used.

UseWorkarea indicates whether the work area for the target monitor is used. When set to True, the form uses the bounds established for the work area instead of the physical monitor. The default value for the parameter is True.

The default value for UseWorkArea was changed from False to True in LCL version 2.3.0. This is the more sensible default value, and it is also Delphi-compatible. The monitor where the form is displayed, or Nil to use the design-time monitor. When True the form is adjusted to the bounds for the WorkArea for the monitor. Otherwise, the form is clipped to the monitor bounds. Returns True if an auto-size action should be skipped when a form handle is not available.

AutoSizeDelayedHandle is an overridden Boolean function used to determine if an AutoSize action must be deferred due to a missing form Handle.

When either Parent or ParentWindow has been assigned, the form is treated like a TWinControl; the return value is set to the value from the inherited method.

If one of the values is unassigned, the return value is always set to False. The form has its own handle, and the resize action does not need to be delayed.

Called from the AutoSizeDelayed method in an ancestor class.

True if an auto-size action should be skipped when a form handle is not available. Marks the form for destruction.

Release is a procedure used to request destruction of the current form instance.

Release checks for a TApplication instance in the Application singleton. When it is assigned (contains a value other than Nil), its ReleaseComponent method is called to free the form instance by posting an asynchronous application message. When Application is not assigned, the Free method is called to destroy the form instance.

True when the form can receive focus.

CanFocus is an overridden Boolean function which indicates if the form instance can receive focus. The return value is True when the form is Visible and Enabled, or the inherited CanFocus method returns True.

CanFocus is used in the implementation of various methods in the class, including: SetWindowFocus, UpdateShowing, SetActiveControl, and Loaded.

True when the form can receive focus in the application. Handles a focus change for a control (enter/exit messages). False when the focused control cannot be changed. The control with focus on the form. Sets the bounds for the restored control.

Ensures that the parameter values are used in the form instance. No actions are performed in the method when ALeft, ATop, AWidth, and AHeight are already assigned to the corresponding properties in the form instance.

Temporarily sets WindowState to wsNormal, and calls SetBounds to apply the parameter values to the form instance. Calls MoveToDefaultPosition when ADefaultPosition is True. Restores WindowState to its original value, and updates the values for the RestoredLeft, RestoredRight, RestoredWidth, and RestoredHeight properties.

Called from the AfterConstruction method prior to signalling the OnCreate event handler and applying the automatic layout policy for the form instance.

Value to restore to the Left property for the form. Value to restore to the Top property for the form. Value to restore to the Width property for the form. Value to restore to the Height property for the form. True if the form is moved to the monitor and location in the Position property. Displays the form instance with support for High DPI scaling.

Show is a method used to display the form in an LCL application. It re-implements the method defined in an ancestor class, and does not call the inherited method.

Show ensures that scaling is performed using the automatic layout policy for the form instance. The PixelsPerInch setting for the Monitor is applied (when needed) by calling the AutoAdjustLayout method. This action is performed when both the Application and the form instance have their Scaled properties set to True.

Show sets the value in the Visible property to True, and calls the ShowWindow routine in the LCL interface at run-time using the Handle and WindowState for the form. The BringToFront method is called to apply the Z-Order for the form instance and its siblings.

TControl.Show Displays the form as a modal Dialog.

Shows the form in a modal state and waits until it is closed by the user or by the program. Modal state means that neither the user nor the program can switch to another form already made visible before calling ShowModal.

The form must have Visible set to False when calling ShowModal. The call does not return until the form is closed. The application switches to modal state until ShowModal has completed.

ShowModal creates its own event loop using ProcessMessages.

Raises an EInvalidOperation exception if the form cannot be displayed as a modal form.

The modal result for the dialog. Displays the form in front of all other forms.

Makes the form Visible and moves it to the top of the Z-Order. WindowState is changed to wsNormal if the form is currently in a minimized state (wsMinimized). Sets the value in Visible to True, and calls BringToFront to move the form to the top of the Z-Order among its siblings.

Returns (and optionally creates) the Handle for the small Icon used for the form. Handle for the small Icon for the form. Executes the specified callback for all child Controls, and Components with no Parent.

GetChildren is an overridden method in TCustomForm which executes the callback method specified in Proc for child Controls owned by Root, or Components which do not have a Parent. It calls the inherited method in TWinControl to execute the callback for Child controls owned by Root. GetChildren iterates over the values in Component, and calls Proc when the HasParent method for a given component returns False.

TWinControl.GetChildren The callback method. Components are enumerated only if Root is Self. Indicates if key messages in a child control are handled in the message processing loop for the form.

Always returns False in TCustomForm.

Returns False in TCustomForm. Control with the key message for the method. Key message from the child control. Adds a handler routine called the first time the form is shown. Used in TAnchorDockHostSite.CreateNew. Handler routine added to the list of fhtFirstShow handlers in the class instance. True if the handler is inserted as the first routine in the list of handlers. False if it is appended to the end of the list. Removes the handler called the first time the form executes its Show method. Not used in the current LCL version. Adds a handler for a form close event.

AddHandlerClose is a method used to add the TCloseEvent handler specified in OnCloseHandler to the list of form handlers for the type. It allows a form instance to have additional event handlers which behave just like the OnClose event handler.

AddHandlerClose calls the AddHandler method to create the TMethod entry used to represent the handler routine. When AsFirst is True, the routine in OnCloseHandler is inserted as the first item in the list of form close handlers.

Applications must implement and assign an object procedure using the signature in TCloseEvent to perform actions needed when the Close or CloseModal method is called for the form instance.

A handler added using AddHandlerClose is signalled after the OnClose event handler for the form instance.

Use RemoveHandlerClose to remove a form close handler added in the method.

Form close handler routine added in the method. True if the handler is stored as the first entry in the list of form close handlers. Removes a form close handler added to the form instance.

RemoveHandlerClose is a method used to remove the form close handler specified in OnCloseHandler from the list of handlers for the type. RemoveHandlerClose reverses the action performed in the AddHandlerClose method.

Form close handler removed in the method. Adds a handler for a form create event.

AddHandlerCreate is a method used to add the TNotifyEvent handler specified in OnCreateHandler to the list of form handlers for the type. It allows a form instance to have additional event handlers which behave just like the OnCreate event handler.

AddHandlerCreate calls the AddHandler method to create the TMethod entry used to represent the handler routine. When AsFirst is True, the routine in OnCreateHandler is inserted as the first item in the list of form create handlers.

Applications must implement and assign an object procedure using the signature in TNotifyEvent to perform actions needed when the form instance has been created and its bounds have been assigned.

A handler added using AddHandlerCreate is signalled after the OnCreate event handler for the form instance.

Use RemoveHandlerCreate to remove a form create handler added in the method.

TNotifyEvent Form create handler added in the method. True if the handler is stored as the first entry in the list of form create handlers. Removes a form create handler added to the form instance.

RemoveHandlerCreate is a method used to remove the form create handler specified in OnCreateHandler from the list of handlers for the type. RemoveHandlerCreate reverses the action performed in the AddHandlerCreate method.

TNotifyEvent Form create handler removed in the method. Returns the currently active MDI child form.

A non-Nil result is returned only when FormStyle contains fsMDIForm or fsMDIChild; otherwise Result is nil.

Nil if the form is neither an MDI host nor child. Nil if the caller is not a MDI form type or a handle has not been allocated for the form. -1 if caller isn't an MDI form or handle is not allocated. Sets scaled to True and calls AutoAdjustLayout with the current PPI for the monitor.

AutoScale is a method used to apply an automatic layout adjustment policy to scale the form and its controls when enabled and needed.

AutoScale sets the value in the Scaled property to True if it is not already enabled. This causes AutoScale to be called again, so no additional actions are performed in the current method call.

AutoScale uses the value in the PixelsPerInch property for the Monitor where the form is displayed to determine if the form and its controls need to be scaled. When Scaled is enabled for the Application, and the run-time PixelsPerInch setting differs from the design-time value, the AutoAdjustLayout method is called. The lapAutoAdjustForDPI policy is applied in the method using scaling factors for the Width and Height values on the form and its Controls.

AutoScale is called when a new value is assigned to the Scaled property.

Docks the form to the specified dock site.

Calls the inherited method using the values in NewDockSite and ARect as arguments.

TControl.Dock Gets the combined Caption for DockClients on the form.

UpdateDockCaption is an overridden method used to get the combined Caption for all DockClients on the form. It does not call the inherited method.

Exclude contains a control which is omitted from the Caption values (when assigned). UpdateDockCaption iterates over the controls in DockClients to build the combined Caption for visible controls (other than the control in Exclude). Blank control captions are ignored. UTF8FixBroken is called to ensure that a given caption does not contain invalid UTF-8 characters. The caption for a TMemo control is truncated after 20 characters.

The Caption values for the controls are concatenated into a comma-delimited list of values which are assigned to the Caption property. An empty string is never assigned to the Caption property.

UpdateDockCaption is called when a new value is assigned to the Text property for a DockClient control with an assigned HostDockSite.

TWinControl.UpdateDockCaption Control to omit from the combined caption value. Indicates if the form is enabled, visible, and has focus.

Active is a read-only Boolean property which indicates if the form is enabled, visible, and has focus.

The SetActive method is used to update the value for the property, locate an ActiveControl for the form, and give focus to the form control. SetActive is called from the WMActivate method when the LM_ACTIVATE window control message is handled for the form.

The value in Active is used in the FocusControl method. It causes SetFocus to be called when its value is False. It is also used in the SetActiveControl method to determine if the window already has focus when the active control is changed.

Specifies the active control on the form.

ActiveControl is a TWinControl property which contains the control which has focus on the form. The property value can be Nil if the form is hidden, disabled, or has never been activated.

Setting a new value for the property causes validity checks to be performed to ensure that the specified control can receive focus when the form is Visible. An EInvalidOperation exception is raised when the new property value contains:

The current form instance.
A control not parented by the current form instance.
A control that returns False from its CanFocus method.

The SetWindowFocus method is called if the form is Active, and the ActiveChanged method is called.

The value in ActiveControl is updated in the FocusControl and DefocusControl methods.

Specifies the active default control on the form.

The active control which is the default control executed when the Enter key is pressed. When setting a new value for the property, a previous default control is notified of the change to the property value using the ActiveDefaultControlChanged method.

Specifies whether files can be dropped onto this form.

AllowDropFiles is a Boolean property which indicates whether this form receives an OnDropFiles event when files are dropped on the form during a drag-and-drop operation.

Allows the form to be drawn with translucency.

AlphaBlend is a Boolean property which indicates if the form can be drawn with translucency. When set to True, the form is drawn with a degree of transparency and diffusion. This allows other forms (and their controls) which have a lower Z-Order value to be seen beneath the form. The default value for the property is False.

Use AlphaBlendValue to specify the degree of transparency and diffusion applied to the form content.

Changing the value in AlphaBlend causes the widgetset class to be notified of the change at run-time when a handle has been allocated for the form instance. A change to the property value is not rendered at design-time.

AlphaBlend and AlphaBlendValue are used in the implementation of the InitializeWnd method, and passed as arguments to methods in the widgetset class when either of the values are changed.

AlphaBlend requires support from both the Desktop Environment (DE) and the hardware for the system; it may not work on all hardware, or platform / operating system combinations supported as Lazarus targets. The translucence level for the form (0=transparent, 255=opaque).

AlphaBlendValue is a Byte property which indicates the level of translucency for the form when AlphaBlend is set to True. AlphaBlendValue must be in the range 0..255 (for the Byte data type), where 0 represents 100% transparency and 255 is for full opacity.

Changing the value for the property causes the widgetset class to be notified of the change in the property value at run-time when a handle has been allocated for the form.

Set AlphaBlend to True to enable translucency for the form.

AlphaBlend and AlphaBlendValue are used in the implementation of the InitializeWnd method, and passed as arguments to methods in the widgetset class when either of the values are changed.

AlphaBlend and AlphaBlendValue require support from both the Desktop Environment (DE) and the hardware for the system; it may not work on all hardware, or platform / operating system combinations supported as Lazarus targets. Indicates if the form can automatically show or hide scroll bars.

AutoScroll is a Boolean property which indicates if the form can automatically show or hide its scroll bars. Set AutoScroll to True to enable scroll bars when the form size is too small to display its content in its entirety. AutoScroll can only be True when the BorderStyle for the form is bsSizeable or bsSizeToolWin, and may be changed to False at run-time when BorderStyle is changed to another value.

Specifies the icons which appear in the title bar for the form.

BorderIcons is a TBorderIcons property which contains valued from the TBorderIcon enumeration, and indicates the icons displayed in the title bar for the form instance. The default value for the property includes the following enumeration values:

biSystemMenu
biMinimize
biMaximize

See TBorderIcon for more information about the enumeration values and their usage.

Changing the value in BorderIcons causes the WidgetSetClass for the form instance to be notified of the new values in the property.

Values in BorderIcons may be automatically changed at run-time when a new value is assigned to the BorderStyle property; see DefaultBorderIcons for the icons used for a specific border style.

The border style affects the title bar, border and resize behavior of the form.

Use BorderStyle to get or set the appearance of the form's border.

By default it is a sizeable window, but it could, for example, be a dialog form or a tool window, or could be non-sizeable.

This property is slightly different (has a different base type) from the TCustomControl.BorderStyle property. When the form is put into another control the window borders depend on the widgetset. There are no borders under GTK.

TFormBorderStyle TBorderStyle TCustomControl.BorderStyle The control associated with the Cancel action.

Determines the control associated with the Cancel action (which exits from the modal form without changing anything). This is usually a button with the caption 'Cancel', but might be an 'Exit' button or anything else the application programmer decides. This control is selected either by explicitly clicking with the mouse, or by hitting the 'Esc' key.

The text displayed in the title bar for the form.

Setting the value in Caption also causes the caption in HostDockSite to be updated.

TControl.Caption TControl.HostDockSite The background color for the form. Color is a TColor property with the background color used for the form. Color is re-declared in TCustomForm to use either clDefault or clBtnFace as the default value for the property. clDefault is used when the UseCLDefault compiler define exists, and indicates that the color is resolved to the value in a Parent control (when assigned). TControl.Color TControl.GetDefaultColor The control associated with the default action for this form.

This is typically a button such as 'Ok' or 'Accept' which is highlighted in some way on-screen to indicate that this is the default action. It is selected either by hitting 'Return' or 'Enter', or by clicking the control with the mouse.

The monitor on which the form is displayed.

Possible values:

dmDesktop: No attempt to choose specific monitor.
dmPrimary: On the primary monitor.
dmMainForm: On the same monitor as the main form. If there is no main form then use dmPrimary behavior.
dmActiveForm: On the same monitor as the currently active form. If there is no active form use dmMainForm behavior.

The designer object when the form is in design mode. Value from ShowInTaskBar adjusted for the default task bar behavior in the application. State flags for the form.

FormState is a read-only TFormState property which contains state flags enabled for the form instance. Values from the TFormStateType enumeration are included in, or excluded from, the set type when corresponding actions occur (or are resolved) for the form instance.

See TFormStateType for more information on the values and meanings in the enumeration.

FormState is updated when properties for the form instance are changed, and in methods which respond to window and control messages in the form instance.

Indicates the style for the form.

Possible values:

fsNormal: Usual style.
fsStayOnTop: Form is positioned above all application's forms, except those which have fsStayOnTop style.
fsSystemStayOnTop: Form is positioned above all OS windows, except other OS top-level windows.
fsSplash: Form is border-less.
fsMDIForm: MDI parent form.
fsMDIChild: MDI child form.

TFormStyle The name of the help file for the form.

HelpFile is a String property which contains the name of the help file for the form instance. HelpFile can use a fully-qualified path to the help file if it is not located in the same directory as the application which implements the form.

The value in HelpFile is used in TApplication when it retrieves the help file name from the active form in the application.

The Icon associated with this Form (in minimized state).

Icon is a TIcon property which contains the graphical icon for the form instance. Icon contains the image displayed on the task bar area when a form is minimized. If an Icon is not explicitly assigned for the form, the icon for the Application is used.

Assigning a new value to Icon causes existing icon handles to be freed, and the widgetset class is notified to re-create the icon handles.

TIcon Allows the form to intercept keystrokes in child controls.

KeyPreview is a Boolean property which controls whether the form can intercept key strokes from child controls.

When KeyPreview is set to True, the form is allowed to receive KeyDown, KeyUp, and KeyPress events before they are received / applied to the ActiveControl in the form. The default value for the property is False.

KeyPreview is used in the implementation of key handling methods in TWinControl. KeyPreview is often enabled for modal dialogs to allow the parent form to handle specific interactions with the user.

Provides indexed access to MDI child forms, when this is a MDI form.

MDIChildren is a read-only indexed TCustomForm property which provides access to the child forms in a Multi-Document Interface (MDI) application. In an MDI application, one of the forms acts as the main form for the application, and is the container for its MDI child forms. In addition, an MDI child form can be nested in another MDI child form.

Historically, support for MDI is dependent on the underlying widgetset or platform. Some widgetsets provide better support for MDI than others. The consensus is that the QT/QT5 widgetsets offers the best level of support for MDI applications.

The form role is determined by the value in the FormStyle property. fsMDIForm is used for the main form, and fsMDIChild for the child forms. MDIChildren is relevant when the current form instance uses one of these MDI form style values.

Index is an Integer value is used to access a MDI child form by its ordinal position in MDIChildren. The return value contains the TCustomForm instance at the specified position, as determined using the GetMDIChildren method in the widgetset class. The return value can be Nil when the current form does not use a FormStyle with the value fsMDIForm or fsMDIChild, or when a handle has not yet been allocated for the form instance. The return value is always Nil at design-time.

Use MDIChildCount to get the number MDI child forms for the form instance.

Use ActiveMDIChild to get the active MDI child form in the application.

Set the value in the FormStyle property to indicate that the class is used as a MDI form.

Ordinal position for the MDI Child form requested. The main menu for the form instance.

Menu is the TMainMenu instance assigned to the form.

Assigning a new value to Menu causes other forms on the Screen to be checked for a duplicate menu assignment. A singular TMainMenu instance cannot be assigned to more than one form. An EInvalidOperation is raised if another form already uses the menu instance. The UpdateMenu method is called when the new property value has been set.

TMainMenu Specifies the return value for a form (or dialog) displayed modally.

ModalResult is a TModalResult property which contains the value derived when the form is displayed modally. Setting a new value for the property causes the widgetset class to be notified when a handle has been allocated for the form.

The value in ModalResult is updated when the ShowModal method is called for the form instance. It may is updated in the CloseModal method when CloseQuery is False and CloseAction is caNone. Finally, it is set to mrCancel in the Close method when FormState contains the value fsModal.

See TModalResult for more information about the enumeration values and their meanings.

The Monitor where the form is shown.

Monitor is a read-only TMonitor property which contains the monitor where the form was displayed. Monitor defaults to the TMonitor instance for the Parent form when it has been assigned.

When the parent form has not been assigned, and a handle exists for the form instance, the widgetset class is notified of the current coordinates for the form. The MonitorFromWindow method in the Screen singleton is called to locate the window closest to the the form (using its handle).

When neither a parent form nor a window handle are available, the MonitorFromPoint method in the Screen singleton is used to locate the form located at the Top and Left coordinates for the form instance.

Tracks changes in the focus for the active form or the last active control for the current form.

LastActiveControl is a read-only TWinControl property used to track a change in the focus for the active form or the control on the current form instance. It is updated when changes are made to the ActiveControl property, or in the SetFocusedControl method.

Defines where popup menus are shown.

PopupMode is a TPopupMode property which controls the display policy for pop-up forms. The default value for the property is pmNone. See TPopupMode for more information about the values and meanings in the enumeration.

Changing the value in PopupMode causes the value in PopupParent to be changed when the property is set to pmAuto or pmNone. At run-time, the widgetset class is notified of the change to the PopupParent property.

PopupMode is used in the implementation of the GetRealPopupParent and ShowModal methods.

Parent form which owns the current form instance when displayed as a pop-up window.

PopupParent is a TCustomForm property which contains the parent form which owns the current form instance when displayed as a pop-up window.

Setting a new value for the property causes the existing pop-up parent form to be removed from the free notifications for the application. A new non-Nil pop-up parent is added to the free notification list, and its PopupMode property is set to pmExplicit.

At run-time, the widgetset class is notified of the change in the PopupParent property. The notification is not performed at design-time.

Handler called when the form receives focus.

This handler is called when the form receives focus for the first time at application start up, and then subsequently each time focus is changed from another window for the same application to this window.

For focus changes between different applications, the Application.OnActivate event handler is called instead.

TApplication.OnActivate Handler called when the form is closed. It determines what happens to the form (destroy, hide...).

OnClose is a TCloseEvent property which represents the event handler signalled when a form calls its Close or CloseModal method.

OnClose is triggered from the DoClose method immediately before calling any internal form handlers registered for the fhtClose form handler action type. OnClose can be used to determine the action performed in subsequent form handlers by setting the value in the CloseAction argument.

An application must implement and assign an object procedure using the signature for TCloseEvent to respond to the event notification.

Event handler signalled when trying to close a form.

OnCloseQuery is a TCloseQueryEvent property which contains the event handler signalled to determine whether the form can be closed. Set the value in the CanClose argument to True to allow the form instance to be closed. The default value for CanClose is True.

Use OnCloseQuery to perform any actions or dialogs needed to confirm that the form can in fact be closed.

An application must implement and assign an object procedure using the signature in TCloseQueryEvent to respond to the event notification.

OnCloseQuery is signalled from the CloseQuery method, and occurs immediately after MDI child forms have called their CloseQuery methods.

Handler called when the form has been created.

OnCreate is a TNotifyEvent property which implements an event handler signalled when a new form instance is created. OnCreate can be used to perform any action needed to configure the new form instance, or update the application where the form is used.

OnCreate is triggered from the DoCreate method (when assigned) before signalling any form handlers using the fhtCreate form handler action type. At this point, the initial coordinates for the form have been assigned, but are not realized until until DoCreate has been completed.

An application must implement and assign an object procedure using the signature for the handler to allow responding to the notification.

TNotifyEvent Handler called when the form is deactivated (loses focus).

OnDeactivate is a TNotifyEvent property which contains an event handler signalled when form is deactivated (loses focus). OnDeactivate is signalled from the Deactivate method (when assigned).

Handler called when the form is destroyed.

OnDestroy is a TNotifyEvent property signalled when the form instance is destroyed. OnDestroy is signalled from the DoDestroy method (when assigned) as one of the steps before destruction of the class instance. Before the event handler is triggered, the form has been hidden and the Menu from the main form in the Application has been unmerged.

Handler called when files have been dropped.

OnDropFiles is a TDropFilesEvent event handler signalled when a File Drag notification is received from the LCL / widgetset interface.

The Sender argument contains the current form instance. The FileName argument contains an array with the file names for the drop operation.

Set AllowDropFiles to True to enable drag and drop operations, and execution of this event handler.

Handler called when Help is requested.

OnHelp is a THelpEvent property which contains the event handler signalled when a Help command is executed for the form instance. Arguments to the event handler identify the command and the context used in the help request.

Command contains the help request type, and corresponds to the values used in the Windows WinHelp API.

Data is a PtrInt type which points the context information for the help request.

The CallHelp argument indicates if handler(s) in the Application instance should be called when the event handler in the form is completed. Set CallHelp to False when the help request has been satisfied in the event handler.

An application must implement and assign an object function using the signature for the handler to respond to the event notification.

Set the return value to True if the Help request was successfully executed.

The OnHelp event handler for the active form is signalled when the TApplication instance executes its DoOnHelp method. The arguments to the event handler contain the values intercepted in the WMHelp message processing for the application. If the OnHelp event handler has not been assigned for the active form, the OnHelp event handler in the Application singleton is signalled (when assigned).

Handler called when the form is being hidden.

OnHide is a TNotifyEvent property that represents the event handler signalled when the form instance is hidden. OnHide is triggered (when assigned) in the DoHide method, and occurs when the CMShowingChanged control message is applied to the Showing property for the form instance.

TWinControl.Showing TNotifyEvent Event handler signalled when the size for the form is changed.

OnResize is a TNotifyEvent property with the event handler signalled when the dimensions for the form have been changed. It is signalled (when assigned) from the DoOnResize method, and occurs in the inherited DoOnResize method in the ancestor class.

Create and assign a procedure to the event handler to perform any actions needed after the form has been resized.

Use the OnConstrainedResize event handler to set the height and/or width for the form using minimum and maximum height and width values.

TControl.OnResize Event handler signalled when a key is pressed, before further handling of the key.

OnShortcut is a TShortcutEvent property that represents the event handler signalled (when assigned) to detect and handle a shortcut key for the form instance. OnShortcut is called from the IsShortcut method used to examine keystroke events intercepted and forwarded by the Application.

The Msg argument contains the key event examined in the handler. Handled indicates that the key is handled by the event when set to True.

Handler called when the form becomes visible.

OnShow is a TNotifyEvent property with the event handler signalled (when assigned) when the form becomes visible. It is signalled from the DoShow method when the CM_SHOWINGCHANGED control messages is handled for the form, and when queued OnResize and OnChangeBounds events are executed for the form.

Create and assign a procedure to OnShow to perform any actions needed when the Visible property for the form is set to True.

Event handler signalled when modal display of the form has been completed.

OnShowModalFinished is a TModalDialogFinished property that implements the event handler signalled when modal display of the form has been completed. An application must implement an object procedure using the signature in TModalDialogFinished, and assign it to the property to respond to the event notification.

Is this still needed? Not used in ShowModal or CloseModal. It does not appear to be signalled anywhere in the current LCL version. Handler called when the form is minimized, maximized or restored.

OnWindowStateChange is a TNotifyEvent property which represents the event handler signalled when the value for the WindowState property is changed. OnWindowStateChange is triggered (when assigned) from the Resizing method, and occurs when the WM_SIZE window message for the action is handled.

See TWindowState for details about the values and meanings in the enumeration.

Uses the font from the Parent when enabled.

If true, the Font will be the same as the one from the Parent. The default value for the property is False in TCustomForm.

While ParentFont is True, all changes to the font in the parent will also be applied to the font for the control. This synchronizes them, keeping them set to the same values. If changes are made directly to the Font property in the control, then ParentFont is automatically be set to False.

TControl.ParentFont The initial placement for the form.

Position is a TPosition property which indicates the size and position policy used to display the form instance. The default value for the property is poDesigned, and indicates that the coordinates used in the form designer are used at run-time. See TPosition for the other values, and their meanings, available for the property.

Changing the value in Position causes the value in AutoSize to be updated when needed, and calls UpdateControlState. No additional actions are performed at design-time.

MoveToDefaultPosition is called when a handle exists for the form instance and the form has not been displayed.

The Left coordinate for the form when it is restored (i.e. changes from minimized or maximized).

RestoredLeft is a read-only Integer property which contains the left coordinate for the form when its size is altered in WMSize or WMMove message handlers. The property value is applied when the asynchronous queued event handler for the form is executed, and calls the DoOnChangeBounds method.

TControl.DoOnChangeBounds TControl.Left The Top coordinate for the form when it is restored (i.e. changes from minimized or maximized).

RestoredTop is a read-only Integer property which contains the top coordinate for the form when its size is altered in WMSize or WMMove message handlers. The property value is applied when the asynchronous queued event handler for the form is executed, and calls the DoOnChangeBounds method.

TControl.DoOnChangeBounds TControl.Left The width of the form when it is resized.

RestoredWidth is a read-only Integer property which contains the Width for the form when its size is altered in WMSize or WMMove message handlers. The property value is applied when the asynchronous queued event handler for the form is executed and calls the DoOnChangeBounds method.

TControl.DoOnChangeBounds TControl.Width The height of the form when it is resized.

RestoredHeight is a read-only Integer property which contains the height for the form when size is altered in WMSize or WMMove message handlers. The property value is applied when the asynchronous queued event handler for the form is executed and calls the DoOnChangeBounds method.

TControl.Height TControl.DoOnChangeBounds How the form is represented in the system Task Bar.

ShowInTaskBar is a TShowInTaskbar property which indicates how the form is represented on the system task bar. The default value for the property is stDefault, and indicates the default behavior for the widgetset, platform, or operating system is used. See TShowInTaskbar for more information about values in the enumeration and their meanings.

ShowInTaskBar is used in conjunction with the TaskBarBehavior property in the Application singleton to determine the effective visibility for the form on the system task bar. For example: The task bar behavior may require grouping related forms under a single form icon.

Changing the value for the property causes the effective visibility to be recalculated when the form is not hidden, or a MDI child form. The new effective task bar visibility is posted to the widgetset class.

Indicates if the control is visible on its parent.

Re-declared in TCustomForm to use a different storage specifier than the ancestor class. In TCustomForm, visibility is not tied to an Action or an ActionLink; it uses the value in the Visible property.

TControl.Visible Indicates whether the form is displayed in a minimized, maximized, full-screen or normal state.

WindowState is a TWindowState property which indicates whether the form is currently displayed minimized, maximized, full-screen or normal (restored) state. The default value is wsNormal (i. e. neither minimized nor maximized).

Changing the value for the property at run-time causes the ShowWindow routine to be called with the Integer display command representing the new property value. The action is not performed at design-time, or when Showing is set to False.

For the Windows platform, wsFullScreen is converted to wsMaximized when calling the ShowWindow API function; the Windows API does not provide a full-screen option. TWinControl.Showing ShowWindow Class reference for the TCustomForm class.

Used primarily in the implementation of window classes for the Lazarus IDE.

Implements a form used in an LCL application.

TForm is a TCustomForm descendant which implements a form displayed in an LCL application. It sets the visibility and default values for properties introduced in ancestor classes. It also adds methods needed for use as an MDI form in an application. LCL version information is available in the LCLVersion property, and is streamed to to the component resource file when a Parent is not assigned for the form.

Forms created at design-time using the Lazarus IDE are TForm descendants. A form can be used as the main form in an application, or it can be displayed as a MDI forms, dialog box, or tool window. Controls can added to the form, such as: TEdit, TLabel, TButton, TCheckBox, TComboBox, TListView, TTreeView, et. al.

Creates an association between the class type and its widgetset class. WSRegisterClass is an overridden class procedure used to register the widgetset class used to create new instances of the form. TCustomForm.WSRegisterClass Creates the handle for the widgetset class and updates it menu and icons.

CreateWnd is an overridden method in TForm. It makes the form instance the main form in the Application singleton if not already assigned and the form is not a MDI Child or a splash form.

CreateWnd calls the inherited method to create (or re-create) the Handle for the widgetset class, set the form state and auto-sizing behavior, and update its Menu and Icons.

Performs actions when LCL component streaming has been completed for the form instance.

Loaded is an overridden method in TForm, and calls the inherited method on entry. It ensures that the value in the LCLVersion property is set to the lcl_version constant from the LCLVersion unit.

Constructor for the class instance.

Create is an overridden constructor for the class instance. Create ensures that the LCLVersion property is updated with the value from the lcl_version constant in the LCLVersion unit. Create calls the inherited constructor prior to exiting from the method.

lcl_version Owner of the form instance. Arranges MDI child forms so they overlap.

Cascade is a method used to arrange MDI Child forms so that they overlap in a cascading fashion.

No actions are performed in the method when FormStyle has a value other than fsMDIForm. At run-time, the Cascade method in the widgetset class is called when its Handle has been allocated.

Use Tile to arrange MDI child forms in a grid format.

Activates the next child MDI form (fsMDIChild) in the form sequence. Activates the previous MDI child form in the form sequence. Arranges MDI child forms side-by-side in a grid format. Arranges the icons for minimized forms in a MDI form.

ArrangeIcons is a method used to arrange the icons for minimized forms on a MDI form. No actions are performed in the method at design-time, or when FormStyle is set to a value other than fsMDIForm. ArrangeIcons calls the corresponding method in the widgetset class when its Handle has been allocated.

TWinControl.Handle TWinControl.HandleAllocated Delimited list of form and / or component properties saved to and restored from an external storage mechanism.

SessionProperties is a String property with the names of properties, in the form instance or its child components. It allows published property values to be saved to and restored from an external storage mechanism like: TIniPropStorage, TXMLPropStorage, or TJSONPropStorage.

Values in the property are delimited using the ';' (SemiColon) character. Component properties require both the component and property names using dotted notation like 'Image1.Visible'. The values can be assigned at design-time using a dialog in the Lazarus IDE, or by setting the property value at run-time.

For example:


// var AForm: TForm;
AForm.SessionProperties := 'Top;Left;WindowState;Image1.Visible;Image1.Transparent';

At design-time, the selection dialog is limited to published properties since RTTI is used to display and access the property values. Use the event handlers in the storage mechanism, or its StoredValues property, to save or restore properties with lesser visibility. Use the Save and Restore methods in the storage mechanism to read and write the property values.

TForm sets the visibility for SessionProperties, introduced in TControl, to published.

TCustomPropertyStorage TIniPropStorage TXMLPropStorage TJSONPropStorage The LCL version number as a String type.

Used to distinguish form streaming content for different versions of the LCL.

Class type used to create new TForm instances.

Class type used to create new TForm instances. Used in the CustomForm package to register a custom form type, unit, or package.

A floating DockSite used to make TControls float. Adds Client as a child control which fills the entire area for the docked form.

DoAddDockClient is an overridden method used to add the control in Client to the docked form. It calls the inherited method on entry to set the Parent in Client to the current class instance. It sets the Align property in Client to alAlign to align the control to the bounds for the docked form. Values in the BorderSpacing property in Client are reset to 0; the current class instance provides the BorderSpacing values for the docked control. At run-time, the Visible property is set to True to display the docked form after the Client has been added.

TWinControl.DoAddDockClient Control added to the docked form instance. Not used in the current implementation. Closes (releases) the form after the last client has been undocked. TWinControl.DoRemoveDockClient Disallows docking of an second client. Tries to make all child controls dockclients. This is of little use in practice, a floating host docksite should have no child controls. Constructor for the class instance.

Create is the overridden constructor for the class instance. It calls CreateNew to create a new form instance, and sets the default values for:

AutoScroll (False)
BorderStyle (bsSizeToolWin)
DockSite (True)
FormStyle (fsStayOnTop)

Owner for the class instance. Indicates if the form can automatically show or hide its scroll bars.

AutoScroll is a Boolean property which indicates if the form can automatically show or hide its scroll bars. The default value for the property is False in TCustomDockForm.

AutoScroll can only be True when the BorderStyle for the form is bsSizeable or bsSizeToolWin, and may be changed to False at run-time when BorderStyle is changed to another value.

TCustomDockForm.BorderStyle TCustomForm.AutoScroll The border style affects the title bar, border and resize behavior of the form.

Use BorderStyle to get or set the appearance of the form's border. The default value in TCustomDockForm is bsSizeToolWin.

This property is slightly different (has a different base type) from the TCustomControl.BorderStyle property. When the form is put into another control the window borders depend on the widgetset. There are no borders under GTK.

TCustomForm.BorderStyle TFormBorderStyle Indicates the style for the form.

The default value in TCustomDockForm is fsStayOnTop.

TCustomForm.FormStyle TFormStyle The pop-up box containing helpful information that appears when the mouse pointer hovers over an object.

THintWindow is a TCustomForm descendant used to display text hints. It is not intended for use with child controls.

Usage:


HintWindow := THintWindow.Create(nil);
Rect := HintWindow.CalcHintRect(0, 'This is the hint',nil);
HintWindow.ActivateHint(Rect, 'This is the hint');

True during ActivateHint. The timer used to make the hint disappear. Adjusts HintRect to fit on the current monitor.

Used in the implementation of the OffsetHintRect method.

Indicates that the width for HintRect should not be decreased. Indicates that the height for HintRect should not be decreased. Collects the flags for Draw Text formatting.

Returns a Cardinal value that contains the Draw Text flags needed for the Alignment and BiDiMode used in the hint window.

Draw Text flags for the hint window. Sets the value for the AutoHide property. THintWindow.AutoHide New value for the property. Hides the hint window when the hint timer has expired.

Called when the hint timer expires. Ensures that the internal hint timer is disabled. Hides the hint window by setting the Visible property to False.

Not used in the method. Sets the value for the HideInterval property. New value for the property. Sets the value for the HintRectAdjust property. New value for the property. Handles the WM_NCHITTEST window message for the hint window.

Sets the result in Message to HTTRANSPARENT. This forces the message to be forwarded to other windowed controls in the Z-Order until a value other than HTTRANSPARENT is returned.

Window message examined and updated in the method. Sets the bounds for the hint window and configures the auto-hide timer.

Sets the bounds for the hint window to the values in the HintRect property, and makes the window Visible. The internal auto-hide timer is enabled when AutoHide contains True.

Called from the ActivateHint method.

TControl.Visible Updates the Window Region fir the hint window.

UpdateRegion calls the SetWindowRgn routine to set the window region for the hint window. The window region contains the area where the system can perform drawing operations; no area outside of the window region can be updated.

SetWindowRgn requires access to the Handle for the hint window; no actions are performed in the method when HandleAllocated returns False.

When UseBGThemes is enabled, ThemeServices are used to get the theme element details needed for the client rectangle in the hint window.

Sets the value for the Color property. TControl.Color New value for the property. Indicates if a background from theme services is used when drawing the hint window. True when ThemeServices are used for the background. Indicates if theme services are used for the foreground rendered for the hint window.

The return value is True when the Font used on the hint window is the stock system font for the platform.

True when ThemeServices are used to draw the foreground for the hint window. Draws the content in the hint window.

Paint is an overridden method in THintWindow. It extends the inherited method to implement default drawing using the Canvas and the settings enabled for theme services. When CountrolCount is 0, the internal routine is used to render the content.When CountrolCount indicates that child controls are present on the hint window, the inherited Paint method is called to render the content.

TCustomControl.Paint System font used to draw text in the hint window. TFont instance for the system font provided by the widgetset. Destructor for the class instance.

Destroy is a class method used as the destructor for the class. Destroy ensures that the reference to the System Font used for hint windows is freed.

Constructor for the class instance.

Create is the overridden constructor for the class instance. Create calls the inherited CreateNew constructor, and allocates resources needed in the class instance. This includes an internal timer used when AutoHide is set to True.

Create sets the default values for the following properties:

Parent: Set to Nil
Color: Set to clInfoBk
Font: Uses the Screen.HintFont
Canvas: Uses the brush style bsClear
Alignment: Set to taLeftJustify
BorderStyle: Set to bsNone
Caption: Set to an empty string ('')
HideInterval: Set to 3000 milliseconds (3 seconds)
AutoHide: Set to False

Create uses the default size from the class type for the control to set the initial bounds for the hint window.

Owner of the class instance. Shows the specified hint.

ActivateHint is an overloaded procedure used to display the Hint text specified in AHint. An overloaded variant allows the display area for the hint window to be specified in the ARect argument.

No actions are performed in the method if ActivateHint has been previously called with the same hint text and display area. Text displayed in the hint window. TRect with the display area for the hint window. Sets the bounds in HintRect and activates the hint window.

ActivateWithBounds is a procedure used to update the location and text for the hint window. ActivateWithBounds sets the value in HintRect to the value in the ARect argument. ActivateWithBounds calls ActivateHint using the value in AHint as the text displayed in the hint window.

Rectangle with the bounds assigned to HintRect. Text displayed in the hint window. An extended version of ActivateHint with additional data used for the hint display.

ActivateHintData is an extended version of ActivateHint. It provides the additional AData argument which contains a pointer to values which can be used to construct the text displayed in the hint window.

The implementation in THintWindow does not use the values in AData. The method must be overridden in a descendent class to use the additional hint data in AData.

Display rectangle for the hint text. Text displayed in the hint window. Pointer to additional data used to construct the hint text. Determines the rectangle required for the hint display.

CalcHintRect determines the display rectangle required for the hint display. CalcHintRect uses the larger of the values in the length of the hint text, and the width of the hint window.

Display area needed for the hint display. Greater than zero, otherwise the full monitor width is used. Hint text used to derive the display area. Pointer to additional data used to construct the hint text. Moves the hint rectangle by the specified amounts. True when the hint rectangle was successfully moved by the specified amounts. TPoint with the horizontal and vertical offsets for the hint display. Additional vertical offset applied to the hint rectangle. Indicates the width for the hint rectangle must be maintained. Indicates the height for the hint rectangle must be maintained. Indicates if the specified message is relevant to a hint window display.

IsHintMsg is a Boolean function used to determine if the message instance in Msg is recognized in THintWindow.

Not used in the current LCL implementation. TMsg True if the message is used for hint windows, False for all other messages. TMsg instance with the message examined in the method. Destroys an allocated handle for the widget.

ReleaseHandle is a method used to free the Handle allocated for the control in the widgetset class. It calls the DestroyHandle method if the Handle has been allocated for the class instance. ReleaseHandle is called by methods in the widgetset class to ensure that the Handle is set 0 (the un-initialized value).

TWinControl.DestroyHandle Applies the argument values to the bounds for the control.

SetBounds is an overridden method in THintWindow. It calls the inherited method on entry to apply the argument values to the bounds for the class instance. It calls the UpdateRegion method to set the window region, or apply a background theme when enabled.

TWinControl.InitializeWnd Value for the Left property. Value for the Top property. Value for the Width property. Value for the Height property. Text alignment used for the hint window.

Alignment is a TAlignment property that indicates the alignment used for the text displayed in the hint window.

The default value for the property is taLeftJustify, as assigned in the Create constructor. The value in Alignment is used to derive the draw text flags required for the BidiMode in the hint display, and passed to to DrawText routine in theme services or widgetset classes.

Contains the bounds used to display the text for the hint.

HintRect is a TRect property which contains the bounds used to display the hint when it is activated. HintRect is adjusted using the values in HintRectAdjust (when assigned) and the borders drawn around the hint display.

Contains the bounds with additional space needed for the hint display. Pointer to data used to formulate text displayed in the hint window. Does the hint disappear (get hidden) after a while?

If AutoHide is TRUE, the hint disappears after an interval specified by HideInterval.

The time after which the displayed hint disappears. Class of THintWindow. For a rendered hint with a child control added by an external provider. Constructor for the class instance. Owner of the class instance. Destructor for the class instance. Shows hint contents are rendered by a provider on child control. Provides information about a physical monitor.

Monitor information is retrieved dynamically from the Operating System. This ensures that any changes to the installed hardware devices or their configuration are taken into account. TMonitor has properties that reflect its dimensions, use as the primary monitor, and its display density (or Pixels per Inch).

TMonitor is the type returned when reading the TScreen.Monitors property. TMonitor is the type used to implement the TCustomForm.Monitor property.

Retrieves monitor information from the OS or platform.

Getinfo is a Boolean function used to get monitor information from the OS or platform hosting the LCL application. Getinfo initializes the Info output parameter to the size required for the TMonitorInfo type, and calls the GetMonitorInfo routine for the widgetset.

The return value is True when monitor information is successfully retrieved for the OS or platform. Info contains the size, display rectangle, work area, and flags for the monitor.

TMonitorInfo True when monitor information was successfully retrieved. TMonitorInfo with values retrieved for the OS or platform. Gets the value for the Left property. Value for the property. Gets the value for the Height property. Value for the Height property. Gets the value for the PixelsPerInch property. Value for the property. Gets the value for the Top property. Value for the Top property. Gets the value for the Width property. Value for the Width property. Gets the value for the BoundsRect property. Value for the BoundsRect property. Gets the value for the WorkareaRect property. Value for the WorkareaRect property. Gets the value for the Primary property. Value for the Primary property. Handle which identifies this monitor to the system. Index of the monitor in the list.

MonitorNum is a read-only Integer property with the ordinal position where the class instance is stored in a list of Monitors. The value for the property is assigned in the UpdateMonitors method in TScreen when the monitor class instance is created and stored.

The left-most screen coordinate for the display.

Left is a read-only Integer property with the coordinate for the left edge of the monitor. It contains the value from the Left member in BoundsRect.

TRect The height for the display.

Height is a read-only Integer property with the height for the monitor in pixels. The property value is calculated as the difference between the Bottom and Top members in BoundsRect.

TRect The top-most screen coordinate for the display.

Top is a read-only Integer property with the top coordinate for the monitor. It contains the value from the Top member in BoundsRect.

TRect The width for the display.

Width is a read-only Integer property with the width for the monitor. It is calculated as the difference between the Right and Left members in BoundsRect.

TRect Rectangle with the dimensions for the monitor.

BoundsRect is a read-only TRect property which contains the bounds for the display device. The property value is assigned from TMonitorInfo information retrieved using the platform-specific GetMonitorInfo routine. The rectangle can be empty (where all members have the value 0) if monitor information was not successfully retrieved from the widgetset.

GetMonitorInfo TMonitorInfo TRect The usable display area on the monitor excluding the system task bar.

WorkareaRect is a read-only TRect property with the bounds for the usable display area on the monitor. This does not include any space covered by the system task bar.

The property value is assigned from TMonitorInfo information retrieved using the platform-specific GetMonitorInfo routine. The rectangle can be empty (where all members have the value 0) if monitor information was not successfully retrieved from the widgetset.

GetMonitorInfo TMonitorInfo TRect Contains True if this is the primary monitor for the system.

Primary is a read-only Boolean property which indicates if the monitor is the primary display in a list of monitors. The property value is determined using flag values in the TMonitorInfo retrieved using GetMonitorInfo for the platform or operating system. It is set to True when the monitor information contains MONITORINFOF_PRIMARY in its flags.

Primary is used when the value for the PrimaryMonitor property is retrieved in the TScreen class. It indicates which TMonitor instance is used as the value for the PrimaryMonitor property.

GetMonitorInfo TMonitorInfo Contains the Pixels Per Inch (or display density) for the monitor.

PixelsPerInch is a read-only Integer property with the display density for the monitor. The property value is determined by calling the GetDpiForMonitor routine for the widgetset to retrieve the effective dots-per-inch for both horizontal and vertical dimensions. The horizontal density is used in the property value.

If the GetDpiForMonitor routine does not complete successfully, the PixelsPerInch property in TScreen is used as the property value.

PixelsPerInch can be used at run-time to ensure that the display density for a Font or Canvas matches the setting in a specific monitor. It is used in the Show and AutoScale methods in TCustomForm to apply an auto-adjust layout policy. It is also used in the form designer for the Lazarus IDE to perform similar actions during component streaming.

TCustomForm.Show TCustomForm.AutoScale A list of monitors available on the system.

TMonitorList is a TList descendant used to store TMonitor class instances representing the physical monitors attached to the system. It provides an indexed Items property that can be used to access monitor information by an ordinal position in the list. It also provides an overridden Notify method to free a TMonitor instance when the lnDeleted list notification is received.

TMonitorList is the type used to implement the Monitors property in TScreen.

TList List notification handler which destroys the Monitor object on removal from the list. The monitor object. The list operation. The indexed list of all Monitors.

Items is a TMonitor property which provides indexed access to a monitor in the list by its ordinal position. Items is the default property for the list, and the target for a list enumerator for the class instance.

TMonitor instances in Items are create and added at run-time when the UpdateMonitors method in TScreen is called. This occurs in response to a WM_DISPLAYCHANGE message in the processing loop for an application.

Ordinal position for a monitor in the list. Contains information about a cursor shape.

TCursorRec is a record type which contains information about a cursor shape used in an application. It contains members with the index position for the cursor, the Handle for the cursor resource, and a pointer to the next cursor record in the list.

Pointer to the next cursor record in the list. Position of the cursor record in the list.. The handle for the cursor resource. Type used for a screen notification handler for form-related events. TObject for the event notification. The affected form. Type for a screen notification handler used for control-related events. TObject for the event notification. The new active control. Screen notification events and handler types. A form was added. A form was removed. The focus moved to another control. The focus moved to another form. The visibility of a form changed. The monitor to use when screen coordinates are outside of the physical bounds for the screens. Default to the nearest monitor. Default to Nil (no suggested monitor). Default to the primary monitor. Provides information about screen displays in an application.

TScreen is a TLCLComponent descendant which provides information about multiple monitors in an LCL application. TScreen allows the GUI for an application to be managed on multiple monitors. It includes the size and resolution for a screen, and allows mapping the virtual Desktop and Workareas to the physical Monitors known to the application.

TScreen also provides access to objects displayed on a given screen, including: Forms, Cursors, and Fonts. For Delphi compatibility, non-visual DataModules are also included in the TScreen information. Properties are provided in the class with the currently active Form, Control and Cursor for a screen.

TScreen is the type used for the Screen singleton in an LCL application.