Several standard controls used in most Lazarus forms TEditCharCase - enumerated type that determines the case of text displayed in the edit box or combobox. Normal mode - Character case according to what the user types. Converts every character that the user types into upper case characters. Converts every character that the user types into lower case characters. TEchoMode - enumerated type that determines how strings in the edit box are displayed. TScrollStyle - enumerated type determining style of scroll bars on a control TScrollCode - the scroll action type.

!!! Beware. The position of these enums must correspond to the SB_xxx values in LCLType (Delphi compatibility, not our decision)

scLineUp,   // = SB_LINEUP
    scLineDown, // = SB_LINEDOWN
    scPageUp,   // = SB_PAGEUP
    scPageDown, // = SB_PAGEDOWN
    scPosition, // = SB_THUMBPOSITION
    scTrack,    // = SB_THUMBTRACK
    scTop,      // = SB_TOP
    scBottom,   // = SB_BOTTOM
    scEndScroll // = SB_ENDSCROLL
Scroll one line up. Scroll one line down. Scroll one page up. Scroll one page down. Scroll to the specified position. Scroll tracking to the specified position. Scroll to the top. Scroll to the bottom. Scroll ends. TScrollEvent - generic event method for processing a scrolling event Determines the scroll action. Contains the current scroll position. TCustomScrollBar : the base class for TScrollBar

The inherited method creates parameters such as caption, style, size and position for a Control

 WinControl.CreateParams CreateParams - calls inherited CreateParams then sets up style and alignment depending on whether horizontal or vertical The paramaeter list

The inherited method creates the interface object, sets parameters and assigns the handle

Then the size of scrollbar, maximum and minimum values, page size and position of scrollbar are set

 TWinControl.CreateWnd CreateWnd - calls inherited CreateWnd then initialises various Scroll Info properties Change - method to signal that a change has occured TControl.Changed The scrolling process The code used for scrolling - up or down a line, a page, to the top or bottom etc The position of the scrolling device TWinControl.Create Create - constructor for TCustomScrollBar: calls inherited Create then initialises size, style and various local variables Defines the Max and Min values, the size of the page and the position of the scroller Kind of scroll bar - whether Horizontal or Vertical LargeChange - the size of the step to be taken by the slider for a large change A LargeChange is produced by the user clicking on the blank area above or below the slider; it is rather analogous to the Page Down or Page Up functions of the Keyboard and is typically set up to move the slider and the contents of the page or canvas by a whole paragraph or half a page or a full page. The maximum value (for bottom of the scroll bar or the right-most extent) The minimum value, for the top of the scroll bar or its left-most extent PageSize: the size of a page - typically used for LargeChange The Position of the scroller along the ScrollBar SmallChange - the size of the step to be taken by the scroller for a small change A small change is produced by the user clicking on one of the triangular tags at either end of the scrollbar. It is rather analogous to the effect of using the up or down arrows on the keyboard, and is typically set to produce a movement of a few pixels or a single line of text OnChange - Event handler for any change in position of the slider or other mouse movement or keyboard event associated with the scrollbar OnScroll - Handler for a scrolling event (by mouse, keyboard or program)

OnScroll - Handler for a scrolling event

Called when there is any movement of the slider by mouse, arrow keys or Page Up/Down keys, or if the display in the main window is caused to scroll

 TScrollBar - a control that allows the user to scroll the current page or document window by moving a slider

TScrollBar - a control that allows the user to scroll the current page or document window by moving a slider

It appears as a long rectangular track or bar within which a smaller contrasting block or slider can move up and down (or from side to side in a horizontal ScrollBar)

It has small triangular indicators or pointers at each end. Typically, for a vertical ScrollBar the top indicator points up, and at the bottom there is a pair of pointers, one up and one down. Clicking with the mouse on one of the pointers moves the slider a small distance (SmallChange) in the specified direction, and the programmer's responsibility is to ensure that the page, image or document in which the ScrollBar is found will scroll by a corresponding small amount

Clicking with the mouse in the blank area of the scrollbar above or below the slider makes the slider move by a larger increment (LargeChange) and scrolls the contents of the window by a larger amount - several lines, a paragraph, half a page or anything up to a page (PageSize)

The slider can also be moved by clicking on it with the mouse, and holding down the button while moving the mouse. The slider follows the mouse until the button is released. If the mouse has a scrollwheel, the slider can be similarly moved by rotating the wheel. In each case, the contents of the window scroll by a corresponding amount

Scrolling of the window and movement of the slider can also be achieved by using the directional arrows or the Page Up/Page Down keys on the keyboard

The location of the slider along the track is held in the Position property, which reports where the mouse has placed it, or can alternatively be set to an arbitrary location by the program. If the mouse or arrow keys are used to move the cursor somewhere on the main window so as to make the display scroll (eg by moving beyond the top or bottom line in a text display) the scroll bar slider moves to indicate the corresponding location along the scroll bar

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

// standard properties, which should be supported by all descendants

Whether the control is Enabled. If not, it usually appears 'greyed-out'

Reads a flag to see whether the control is enabled, or stores a new value. If stored, sets a flag to say so.

 A LargeChange is produced by the user clicking on the blank area above or below the slider; it is rather analogous to the Page Down or Page Up functions of the Keyboard and is typically set up to move the slider and the contents of the page or canvas by a whole paragraph or half a page or a full page. // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu A small change is produced by the user clicking on one of the triangular tags at either end of the scrollbar. It is rather analogous to the effect of using the up or down arrows on the keyboard, and is typically set to produce a movement of a few pixels or a single line of text Reads or writes information in flag; default is -1 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility.

OnKeyDown - event handler for instance when key is down while control has focus

Differs from OnKeyPress in that the key may have already been down when the control received focus; with OnKeyPress the key needs to become pressed while the control has focus.

OnKeyPress - event controller for a key being pressed while the control has focus

Differs from OnKeyDown in that the key needs to become pressed while the control has focus; with OnKeyDown the key may have already been down when the control received focus.

OnKeyUp - event handler for instance when a key is up (not pressed) while the control has focus

The key may already have been up when the control received focus, or a pressed key may become released during the time the control has focus.

OnScroll - Handler for a scrolling event

Called when there is any movement of the slider by mouse, arrow keys or Page Up/Down keys, or if the display in the main window is caused to scroll

 TCustomGroupBox - the base class for TGroupBox, TRadioGroup and TCheckGroup GetControlClassDefaultSize - sets its own defaults, overriding the inherited values TControl.GetControlClassDefaultSize Create - constructor for TCustomGroupBox: calls inherited Create then initialises style and bounds TWinControl.Create TGroupBox - a container that allows a number of objects to be grouped physically and conceptually on the form

Group Box. Allows a number of objects to be grouped physically and conceptually on the form; they can be moved around together and have certain properties in common.

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

Reads values from flag or stores values to flag. Most of the properties are inherited from TControlChildSizing,
which you should read to find out more about this control

// standard properties, which should be supported by all descendants

Finds or sets the client height, and sets a flag if it has been stored

// standard properties, which should be supported by all descendants

ClientWidth - determines the width of the client within which the control exists; reads the width of the client control or sets the value. Sets flag if value is stored

// standard properties, which should be supported by all descendants

Reads the value for colour, or stores the value, and sets a flag if the colour is stored.

The default colour is the same as the window in which the control is located.

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

 Reads or sets a flag to show whether this is a dock site. Default false

// standard properties, which should be supported by all descendants

Whether the control is Enabled. If not, it usually appears 'greyed-out'

Reads a flag to see whether the control is enabled, or stores a new value. If stored, sets a flag to say so.

// standard properties, which should be supported by all descendants

Reads a flag to see what font should be used, or sets a flag to store it. If stored, sets a flag to say so

The properties of Font are defined in the parent class TFont

// standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu // standard properties, which should be supported by all descendants
Reads flag or writes one to determine if a hint is to be shown when mouse hovers over this control. If value is stored, a storage flag is set. Display of the actual hint is controlled by OnShowHint Reads or writes information in flag; default is -1

Reads or writes boolean flag; default is False

Use the TabStop to allow or disallow access to the control using the Tab key.

If TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't use the Tab key to move to the control.

 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility.

// standard properties, which should be supported by all descendants

Reads or Writes flag if bounds are changed

// standard properties, which should be supported by all descendants

This is often the default action for many controls, and is often the ONLY action specified by the programmer. The action can be spcified by the user, either by typing explicit code into the implementation section for this control, or by selecting an action from a pre-supplied ActionList

Reads or writes a flag if a mouse click is detected, and sets a flag if a value is stored.

Double-clicking is much more common in a Windows environment than in Unix or Linux, where single-clicking is the default method for selecting an object. However, in all environments there could be valid use for a double-click, and a method should be supplied if appropriate.

OnKeyDown - event handler for instance when key is down while control has focus

Differs from OnKeyPress in that the key may have already been down when the control received focus; with OnKeyPress the key needs to become pressed while the control has focus.

OnKeyPress - event controller for a key being pressed while the control has focus

Differs from OnKeyDown in that the key needs to become pressed while the control has focus; with OnKeyDown the key may have already been down when the control received focus.

OnKeyUp - event handler for instance when a key is up (not pressed) while the control has focus

The key may already have been up when the control received focus, or a pressed key may become released during the time the control has focus.

 // standard properties, which should be supported by all descendants
Reads or Writes flag if control is re-sized. TComboBoxAutoCompleteTextOption - Enumerated type that defines the behavior of the AutoComplete feature in a combobox control.

TComboBoxAutoCompleteTextOption defines the behavior of the AutoComplete feature.

  • cbactEnabled: Enable Auto-Completion feature.
  • cbactEndOfLineComplete: Perform Auto-Complete only when cursor is at the end of the string.
  • cbactRetainPrefixCase: Retains the case of characters user has typed. (This option has no effect if cbactEndOfLineComplete is False)
  • cbactSearchCaseSensitive: Search completion string with case sensitivity.
  • cbactSearchAscending: Search completion string in ascending order. (False will search in descending order)
 TComboBoxAutoCompleteText - Set of TComboBoxAutoCompleteTextOption ComboBox Style - enumerated type for style of combobox ComboBox Style: may be Simple, a single-line Drop-Down or a Drop-Down list, or some version drawn by the Owner TCustomComboBox - the base class from which TComboBox is derived

TCustomComboBox - the base class from which TComboBox is derived

Despite similarities in appearance to TCustomEdit and TCustomList , the class inherits no properties from these classes, but only from TWinControl

It has some interesting properties including AutoComplete and AutoCompleteText, AutoDropDown and the ability to create and add a History display

 FCharCase: TEditCharCase FAutoCompleteText: TComboBoxAutoCompleteText Private variable of property AutoCompleteText. Options for behavior of the Auto-Complete feature. FAutoSelect: Boolean

Private variable for property AutoSelect. When True, the edit control will select all its text when:

  • It receives focus
  • The Enter key is pressed.
  • A new item is selected.
 FAutoSelected: Boolean Private variable for property AutoSelected. True indicate that the edit or combobox control has just performed an AutoSelect operation so that subsequent mouse-clicks and keystrokes proceed normally without selecting the text. False is set when the edit or combobox control loses focus. Combo Box SetItems writes the strings specified in Value to the Items list

Inherited method works out the correct bounds, sets style, fonts and colours, performs any pending resize operations

 TWinControl.InitializeWnd InitializeWnd - creates the underlying interface-object: calls inherited InitializeWnd then sets up several local lists and variables notably for style and size

Inherited method removes handles and restores colour and font flags

 TWinControl.DestroyWnd DestroyWnd - finds somewhere to store locally held variables then frees lists, calls inherited DestroyWnd DoEnter - cals inherited method then autoselects text in dropdown list if required TWinControl.DoEnter DoExit - disables AutoSelect then calls inherited DoExit TWinControl.DoExit DrawItem - perform the action necessary to draw the specified indexed item at the specified position

DrawItem - perform the action necessary to draw the specified indexed item at the specified position

Software emulation of OnDrawItem event

 GetControlClassDefaultSize - sets its own defaults, overriding inherited values TControl.GetControlClassDefaultSize LMChanged - LCL Message to signify that the control has changed Change - software emulation of OnChange event Select - software emulation of OnSelect event DropDown - software emulation of OnDropDown event CloseUp - software emulation of OnCloseUp event AdjustDropDown - adjust the properties of the DropDown list GetItemCount - returns the number of items in the DropDown list GetItemHeight - returns the height of the current list item GetSelLength - returns the length of the current selection GetSelStart - returns the start position of the current selection GetSelText - returns the currently selected text string GetItemIndex - returns the Index value of the current list item GetMaxLength - returns the maximum length of a list item IsReadOnlyStored - returns True if ReadOnly status is stored SetDropDownCount - writes the number of items in DropDown list to local variable SetDroppedDown - writes DroppedDown status to local boolean variable SetItemHeight - writes height of current list item to local variable SetItemIndex - writes index value of current item to local variable SetMaxLength - writes maximum length of list item to local variable SetSelLength - writes length of current selection to local variable SetSelStart - writes start position of current selection to local variable SetSelText - writes currently selected text string to local variable SetSorted - writes to local (boolean) variable to show if list is Sorted SetStyle - writes the current Style specifier to local variable RealSetText - sets the ComboBox text to the caption value specified

If the text AValue occurs in the list of strings, then sets the Itemindex, otherwise does the default action which is to store text as a string rather than performing read-write to a PChar buffer

 TControl.RealSetText KeyDown - performs code for traversing the dropdown list to the correct location before calling inherited KeyDown

The inherited method provides software emulation of the event handler OnKeyDown which acts if a key has been pressed and is still down

 TWinControl.KeyDown KeyUp calls inherited method then performs specific actions depending on which key is being processed

The inherited method provides software emulation for the OnKeyUp event.

 TWinControl.KeyUp KeyPress adjusts character case if necessary then calls inherited method

The inherited method provides software emulation of the OnKeyPress event, which acts when a key is pressed.

The OnKeyPress event handler is usually provided by the application programmer as a specific action to be performed when the event occurs; it often contains a case statement or similar choice structure to divert execution along specific pathways in response to pressing different keys

 TWinControl.KeyPress MouseUp calls inherited method then sets AutoSelect if left mouse button is clicked for the first time after receiving focus

The inherited method allows the programmer to simulate the action to be taken when the mouse is in the Up position over the specified control. It is usually a programmer-supplied method similar to the OnMouseUp event handler.

 TControl.MouseUp SelectItem - returns True if current item (specified by a string) is to be selected DropDownCount - number of entries in the drop-down list ItemHeight - the height of the current item in the drop-down list ItemWidth - the width of the current item in the drop-down list MaxLength - the maximum allowed length of a string OnChange - event handler for any change in properties of the combo box OnCloseUp - event handler for when the drop-down box is closed up again OnDrawItem - event handler for when an entry is written to the Items list OnDropDown - event handler for when the drop-down list appears Event handler when items can be just-in-time populated before showing the drop-down list. Event handler when measurement of an item is required Event handler when an item or some text is selected Sorted - whether the entries in the drop-down list have been sorted TWinControl.Create Create - constructor for TCustomComboBox: calls inherited Create then initialises styles, item lists, bounds and various other local variables TWinControl.Destroy Destroy - destructor for TCustomComboBox: frees handles, itemlists, canvas and items then calls inherited Destroy IntfGetItems - gets list of items from the interface AddItem - adds an Item to the list in the drop-down box AddHistoryItem - Add an Item as first entry in History List

AddHistoryItem - Add an Item as first entry in History List

Removes the Item from old position and removes last item if history is full

 The item to be addd to the list The maximum number of items that can be added to the history Whether the item is to be set as text Whether the item is added in a case sensitive manner (eg determines how they are sorted) The history item to be added, expressed as an object Clear - remove all text and drop-down list ClearSelection - clear the currently selected text or items from drop-down list CharCase: indicates whether text is to be displayed as Upper, Lower or Normal case (as entered)

Indicates how text is displayed in a text editing control in the following ways:

  • Normal case letters
  • Upper case letters
  • Lower case letters
 DroppedDown - indicates whether or not the drop-down list has appeared Measure the size (Height) of an item in the drop-down list The index number of the item whose height is to be measured The height as measured by the procedure Select all items in the list AutoComplete - enables the facility to offer suggestions for completing text-strings AutoCompleteText : Options for behavior of the Auto-Complete feature

AutoCompleteText : Options for behavior of the Auto-Complete feature

  • Enabled: Enable Auto-Completion feature.
  • EndOfLineComplete: Perform Auto-Complete only when cursor is at the end of the string.
  • RetainPrefixCase: Retains the case of characters user has typed. (This option has no effect if cbactEndOfLineComplete is False)
  • SearchCaseSensitive: Search completion string with case sensitivity.
  • cbactSearchAscending: Search completion string in accending order. (False will search in descending order)

This property exists as a Set of Options, so zero or more options may be operational

 AutoDropDown - if True, the drop-down list appears as soon as the cursor moves over the text box

AutoDropDown - if True, the drop-down list appears as soon as the cursor moves over the text box

If False, the drop-down box only appears when the downward triangular indicator at the end of the box is selected

 AutoSelect : Boolean. If True, all contents of Text box are selected when control receives focus

When True, the edit control will select all its text when:

  • It receives focus
  • The Enter key is pressed.
  • A new item is selected.
 AutoSelected : True indicates that the combobox control has just performed an AutoSelect operation

True indicates that the combobox control has just performed an AutoSelect operation so that subsequent mouse-clicks and keystrokes proceed normally without selecting the text.

False is set when the combobox control loses focus.

 ArrowKeysTraverseList - enables the operator to use the keyboard Arrow keys to move through the list as an alternative to using the mouse Canvas - the area on which the components are drawn or painted Items - an array of strings that holds the entries of the drop-down list Index - the number of the currently selected item (starting at zero)

Index - the number of the currently selected item

The first item has number 0, the second has number 1, the third number 2, etc.

In case no item is selected, ItemIndex has value -1.

 ReadOnly - if True, information in the control can only be Read, not Written or Deleted SelLength - the length of the text that has been selected in bytes SelStart - if text is selected this is the starting position otherwise the cursor position in bytes starting at 0 SelText - the text string that has been selected for editing Style : may be Simple, a single-line Drop-Down or a Drop-Down list, or some version drawn by the Owner Text - the string appearing in the main box. If an item on the drop-down list is selected, it replaces the contents of Text

Reads or writes boolean flag; default is False

Use the TabStop to allow or disallow access to the control using the Tab key.

If TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't use the Tab key to move to the control.

 TComboBox - a simple combination of text box for free text entry, and a drop-down list allowing one of several options to be chosen.

TComboBox - a simple combination of text box for free text entry, and a drop-down list allowing one of several options to be chosen.

The default text-string (if any, entered in the Form Designer) and the value of the text string that is ultimately selected from the drop-down list, is held in Text

The values that can be selected from the drop-down list are held in the string-array Items. Clicking on the ellipsis (...) next to Items in the Object Inspector opens a pop-up string-list editor which allows the designer to enter and edit a number of lines of text to represent the selections

At run-time, the entry selected from the drop-down list in Items is used to replace any information previously found in Text, and ItemIndex holds the (zero-origin) index number of the selected item

If no value is selected from the drop-down list, the default text (if any) remains, or any information typed directly into Text will be returned, and ItemIndex takes the value of -1

 Align the Control with other Controls in its vicinity Anchors

// standard properties, which should be supported by all descendants

AutoSize permits the size of a control to be adjusted automatically, for example a button can become bigger or smaller to accommodate a longer or shorter caption.

Reads logical (boolean) flag to see whether auto-sizing is to be operated, or writes the flag to say it should be done. Default is false, ie no auto-sizing

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

 Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

Indicates how text is displayed in a text editing control in the following ways:

  • Normal case letters
  • Upper case letters
  • Lower case letters

// standard properties, which should be supported by all descendants

Reads the value for colour, or stores the value, and sets a flag if the colour is stored.

The default colour is the same as the window in which the control is located.

// standard properties, which should be supported by all descendants

Whether the control is Enabled. If not, it usually appears 'greyed-out'

Reads a flag to see whether the control is enabled, or stores a new value. If stored, sets a flag to say so.

// standard properties, which should be supported by all descendants

Reads a flag to see what font should be used, or sets a flag to store it. If stored, sets a flag to say so

The properties of Font are defined in the parent class TFont

Index - the number of the currently selected item

The first item has number 0, the second has number 1, the third number 2, etc.

In case no item is selected, ItemIndex has value -1.

// standard properties, which should be supported by all descendants

Reads or Writes flag if bounds are changed

// standard properties, which should be supported by all descendants

This is often the default action for many controls, and is often the ONLY action specified by the programmer. The action can be spcified by the user, either by typing explicit code into the implementation section for this control, or by selecting an action from a pre-supplied ActionList

Reads or writes a flag if a mouse click is detected, and sets a flag if a value is stored.

Double-clicking is much more common in a Windows environment than in Unix or Linux, where single-clicking is the default method for selecting an object. However, in all environments there could be valid use for a double-click, and a method should be supplied if appropriate.

OnKeyDown - event handler for instance when key is down while control has focus

Differs from OnKeyPress in that the key may have already been down when the control received focus; with OnKeyPress the key needs to become pressed while the control has focus.

OnKeyPress - event controller for a key being pressed while the control has focus

Differs from OnKeyDown in that the key needs to become pressed while the control has focus; with OnKeyDown the key may have already been down when the control received focus.

OnKeyUp - event handler for instance when a key is up (not pressed) while the control has focus

The key may already have been up when the control received focus, or a pressed key may become released during the time the control has focus.

 // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu // standard properties, which should be supported by all descendants
Reads flag or writes one to determine if a hint is to be shown when mouse hovers over this control. If value is stored, a storage flag is set. Display of the actual hint is controlled by OnShowHint Reads or writes information in flag; default is -1

Reads or writes boolean flag; default is False

Use the TabStop to allow or disallow access to the control using the Tab key.

If TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't use the Tab key to move to the control.

 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility. TListBoxStyle - enumerated type for style of listbox TSelectionChangeEvent - generic procedure type for selection change event TCustomList Box : the base class for TListBox Clear the selected items AssignItemDataToCache - assigns data for the item, specified by a pointer AData, to a cache AssignCacheToItemData - assigns the cache to the item data specified by the pointer AData Loaded calls inherited method then sends the item index value to the handle TComponent.Loaded TWinControl.Loaded InitializeWnd calls inherited method then sets up the list of strings TWinControl.InitializeWnd FinalizeWnd frees the list of strings then calls inherited method TWinControl.FinalizeWnd GetControlClassDefaultSize sets its own defaults, overriding inherited values TControl.GetControlClassDefaultSize CheckIndex - check that the supplied index refers to valid data GetItemHeight - returns a value for the height of an item GetItemIndex - returns an index value for the current list item GetSelCount - returns the number of selected items GetSelected - returns True if the specified indexed item has been selected GetCachedDataSize - returns the amount of data needed per item GetCachedData - returns a pointer to the data corresponding to the supplied index SetExtendedSelect - specifies a boolean indicator to show whether Extended Selection is permitted SetItemIndex - specifies an item index SetItems - specifies the string values of the items SetItemHeight - specifies the height of an item SetMultiSelect - specifies whether multiselect is permissible (ie select multiple entries by holding down Shift or Ctrl keys) SetSelected - specifies the Selected property of the indexed item SetSorted - specifies whether the list is sorted SetStyle - specifies the style of the listbox DrawItem - method to draw the nominated indexed item in the specified rectangle DoSelectionChange - perform a change in the selection SendItemIndex - transmit the item index to the system Event handler when an item requires to be measured TWinControl.Create Create - constructor for TCustomListBox: calls inherited Create then initialises style, canvas, item list and various other local variables TWinControl.Destroy Destroy: destructor for TCustomListBox: frees canvas and item list, then calls inherited Destroy Find the index at the Y coordinate The integer value of the Y coordinate Get the selected text string Returns the index value of the item at the specified position Returns the coordinates of the rectangle in which the item lies Is the item with the specified index visible? Is the item with the specified index fully visible (or is part of it outside the bounds of the visible window)? MakeCurrentVisible - makes the current item visible Measure the height of the item in the list with the specified index The index value of the item to be measured The height of the item as measured by the procedure Clear the listbox - both the edit box and the drop-down list Lock ( make permanent) the change in the selection Unlock the previously locked change in selection

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

Canvas - defines the area on which all graphic material is drawn Performs Click procedure when the selection is changed (which usually puts the selected item into the edit box) Columns - the number of vertical columns in which the Items are arranged

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

 Count - the number of entries in the list of Items

Count - the number of entries in the list of Items

For Delphi compatability

 ExtendedSelect - boolean. Whether extended selection is allowed. Default True

// standard properties, which should be supported by all descendants

Reads a flag to see what font should be used, or sets a flag to store it. If stored, sets a flag to say so

The properties of Font are defined in the parent class TFont

not implemented ItemHeight - the height of the individual Items ItemIndex: Integer to indicate the currently selected item (zero origin) Indicates the currently selected item. The first item has number 0, the second has number 1, the third number 2, etc. In case no item is selected, ItemIndex has value -1. If MultiSelect is True, ItemIndex represents the item which has focus, which typically has a different color from the other items. Items - an array of strings representing the list of entries MultiSelect - allows more than one Item from the list to be selected at a time, by pressing the CTRL or SHIFT key while selecting

// standard properties, which should be supported by all descendants

Reads or Writes flag if bounds are changed

// standard properties, which should be supported by all descendants

This is often the default action for many controls, and is often the ONLY action specified by the programmer. The action can be spcified by the user, either by typing explicit code into the implementation section for this control, or by selecting an action from a pre-supplied ActionList

Reads or writes a flag if a mouse click is detected, and sets a flag if a value is stored.

Double-clicking is much more common in a Windows environment than in Unix or Linux, where single-clicking is the default method for selecting an object. However, in all environments there could be valid use for a double-click, and a method should be supplied if appropriate.

 OnDrawItem - event handler for drawing an Item

OnDrawItem - event handler for drawing an Item

For example, selecting an item may require it to be highlighted or have its font or background changed

OnKeyDown - event handler for instance when key is down while control has focus

Differs from OnKeyPress in that the key may have already been down when the control received focus; with OnKeyPress the key needs to become pressed while the control has focus.

OnKeyPress - event controller for a key being pressed while the control has focus

Differs from OnKeyDown in that the key needs to become pressed while the control has focus; with OnKeyDown the key may have already been down when the control received focus.

OnKeyUp - event handler for instance when a key is up (not pressed) while the control has focus

The key may already have been up when the control received focus, or a pressed key may become released during the time the control has focus.

 // standard properties, which should be supported by all descendants
Reads or Writes flag if control is re-sized. OnSelectionChange - event handler for changing the Item selected // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu The number of selected iems in the drop-down list Selected - whether the Item with given Index has been selected // standard properties, which should be supported by all descendants
Reads flag or writes one to determine if a hint is to be shown when mouse hovers over this control. If value is stored, a storage flag is set. Display of the actual hint is controlled by OnShowHint Sorted - whether the selected Items in the list have been arranged in alphabetical order Style of List Box - normal, owner-draw fixed, or owner-draw variable Reads or writes information in flag; default is -1

Reads or writes boolean flag; default is False

Use the TabStop to allow or disallow access to the control using the Tab key.

If TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't use the Tab key to move to the control.

 Topindex - the highest value of Index in this list 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility. TListBox : a simple string list from which a choice is made

TListBox : a simple string list from which a choice is made

The array of strings is held in Items

Clicking on the ellipsis (...) next to the Items entry in the Object Inspector at design-time opens a string-list editor in which the individual text-strings for the list can be entered or edited. The editor also allows the entries to be sorted alphabetically in normal or reverse order.

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

// standard properties, which should be supported by all descendants

Reads the value for colour, or stores the value, and sets a flag if the colour is stored.

The default colour is the same as the window in which the control is located.

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

// standard properties, which should be supported by all descendants

Whether the control is Enabled. If not, it usually appears 'greyed-out'

Reads a flag to see whether the control is enabled, or stores a new value. If stored, sets a flag to say so.

// standard properties, which should be supported by all descendants

Reads a flag to see what font should be used, or sets a flag to store it. If stored, sets a flag to say so

The properties of Font are defined in the parent class TFont

// standard properties, which should be supported by all descendants

Reads or Writes flag if bounds are changed

// standard properties, which should be supported by all descendants

This is often the default action for many controls, and is often the ONLY action specified by the programmer. The action can be spcified by the user, either by typing explicit code into the implementation section for this control, or by selecting an action from a pre-supplied ActionList

Reads or writes a flag if a mouse click is detected, and sets a flag if a value is stored.

Double-clicking is much more common in a Windows environment than in Unix or Linux, where single-clicking is the default method for selecting an object. However, in all environments there could be valid use for a double-click, and a method should be supplied if appropriate.

OnDrawItem - event handler for drawing an Item

For example, selecting an item may require it to be highlighted or have its font or background changed

OnKeyPress - event controller for a key being pressed while the control has focus

Differs from OnKeyDown in that the key needs to become pressed while the control has focus; with OnKeyDown the key may have already been down when the control received focus.

OnKeyDown - event handler for instance when key is down while control has focus

Differs from OnKeyPress in that the key may have already been down when the control received focus; with OnKeyPress the key needs to become pressed while the control has focus.

OnKeyUp - event handler for instance when a key is up (not pressed) while the control has focus

The key may already have been up when the control received focus, or a pressed key may become released during the time the control has focus.

 // standard properties, which should be supported by all descendants
Reads or Writes flag if control is re-sized. // standard properties, which should be supported by all descendants
Reads or Writes a flag when a hint (a small pop-up box, appearing when the mouse hovers over an object) is to be shown Event handler for start of dragging process ParentBiDiMode - does the control follow the BiDiMode settings of its parent? ParentShowHint - does the control adopt the same hinting behaviour as its parent? Default is true // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu // standard properties, which should be supported by all descendants
Reads flag or writes one to determine if a hint is to be shown when mouse hovers over this control. If value is stored, a storage flag is set. Display of the actual hint is controlled by OnShowHint Reads or writes information in flag; default is -1

Reads or writes boolean flag; default is False

Use the TabStop to allow or disallow access to the control using the Tab key.

If TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't use the Tab key to move to the control.

 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility. TCustomEdit : the base type from which the TEdit Box is derived.

TCustomEdit : the base type from which the TEdit Box is derived.

This control deals, for example, with issues such as selection of text sub-strings within the whole text string which are to be edited (cut, pasted, deleted, highlighted etc)

 FAutoSelect: Boolean

Private variable for property AutoSelect.

When True, the edit control will select all its text when:

  • It receives focus
  • The Enter key is pressed.
  • A new item is selected.
 FAutoSelected: Boolean Private variable for property AutoSelected. True indicate that the edit or combobox control has just performed an AutoSelect opertation so that subsequent mouse-clicks and keystrokes proceds normally without selecting the text. False is set when the edit or combobox control loses focus. FCharCase: TEditCharCase

Private variable for property CharCase. Indicates how text is displayed in a text editing control.

  • Normal case letters
  • Upper case letters
  • Lower case letters
 SetReadOnly - specifies whether ReadOnly applies

CalculatePreferredSize - find default/preferred height and width

procedure TControl.CalculatePreferredSize

(var PreferredWidth, PreferredHeight: integer; WithThemeSpace: Boolean);

Calculates the default/preferred width and height for a control, which is used by the LCL autosizing algorithms as default size. Only positive values are valid. Negative or 0 are treated as undefined and the LCL uses other sizes instead.

TWinControl overrides this and asks the interface for theme dependent values. See TWinControl.CalculatePreferredSize for more information.

WithThemeSpace: If true, adds space for stacking.

For example: TRadioButton has a minimum size. But for stacking multiple TRadioButtons there should be some space around. This space is theme dependent, so the parameter is passed to the widgetset.

 CreateWnd - calls inherited CreateWnd, then initialises various properties relevant to the Widget Set in use TWinControl.CreateWnd Change - software emulation of the OnChange event DoEnter - sets AutoSelect if required then calls inherited method TWinControl.DoEnter DoExit - disables AutoSelect then calls inherited method TWinControl.DoExit GetSelLength - returns the length of the selected text GetSelStart - returns the position of the start of the selection GetSelText - returns the selected text string SetEchoMode - specifies the echo mode SetSelLength - specifies the length for the selected text SetSelStart - specifies the position for the start of selection SetSelText - specifies the selected text string GetControlClassDefaultSize returns its own defaults, overriding inherited values TControl.GetControlClassDefaultSize KeyUp calls inherited method then processes according to the identity of Key TWinControl.KeyUp AutoSelect : if True, the edit control will select all its text when it receives focus or when the Enter key is pressed. AutoSelected : if True, indicates that the edit control has just performed an AutoSelect operation

If True, indicates that the edit control has just performed an AutoSelect operation so that subsequent mouse-clicks and keystrokes proceed normally without selecting the text.

False is set when the edit control loses focus.

 TWinControl.Create Create - constructor for TCustomEdit: calls inherited Create then initialises style, colour, size and various other local variables Clear - delete all text SelectAll text, for example in order to copy or delete it ClearSelection - delete all characters in selected text CopyToClipboard - put a copy of the selection on the clipboard, while leaving the original text in place CutToClipboard - remove the selected text from its original location and put it on the clipboard PasteFromClipboard - put a copy of the clipboard contents at the current writing position CharCase - rules for what case to use (upper or lower) to display text

Indicates how text is displayed in a text editing control in the following ways:

  • Normal case letters
  • Upper case letters
  • Lower case letters

The rules can, of course, be overridden by use of the shift key.

 EchoMode - how to echo keypresses on screen: normal (returning the actual character for that key), all upper or lower case, or a masking character as used in entering passwords MaxLength: maximum length allowed for text string MaxLength determines the maximum number of characters allowed in a TCustomEdit. When its value is 0, the user is allowed to enter any number of characters. Unlike VCL, if a text set through the Text property has more characters then MaxLength it will be truncated. It's not possible to implement the VCL behavior due to characteristics of non win32 widgetsets. Whether the text has been modified Modified: has the text been modified since creation? OnChange - event handler for any change in text PasswordChar : the character which appears in the Edit box replacing and masking the actual character typed

PasswordChar : the character which appears in the Edit box replacing and masking the actual character typed.

Typically used in password input, to prevent the typed characters from being seen by passers-by or casual observers (or even malicious observers!)

 // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu ReadOnly - the contents of the edit box may only be read, not written or erased SelLength : the length (in characters) of the text that has been selected for editing Sel Start: the index of the character from which selection (for editing) begins Sel Text : the string within the edit control that has been selected for editing Reads or writes information in flag; default is -1

Reads or writes boolean flag; default is False

Use the TabStop to allow or disallow access to the control using the Tab key.

If TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't use the Tab key to move to the control.

 Text : the character string contained in the Edit Box Text : the character string contained in the Edit Box TMemoScrollBar - a Scroll Bar specifically for use in Memo Boxes Scroll Bar specifically for use in Memo Boxes. Inherits most of its properties from its ancestor, TControlScrollBar The amount by which the scroll indicator moves if the triangle at either end of the bar is selected.
Read or write a flag to determine the increment, an integer with a default value of 8 (pixels) 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.
Reads or writes a flag to determine paging increment; default value is 80 pixels Reads or writes a flag to determine smooth scrolling, and sets a flag is the scrolling status is stored Reads or writes a flag with the position; default is zero Reads or writes a flag to determine the range; default is zero Reads or writes a flag to determine the size; by default the size is not stored Reads or writes flag to determine visibility, and sets a flag if the property is stored TCustomMemo : the base class for TMemo CreateHandle calls inherited method then initialises Lines TWinControl.CreateHandle DestroyHandle frees Lines then calls inherited method TWinControl.DestroyHandle RealGetText - returns the contents of Lines.Text (overriding inherited method) TControl.RealGetText Returns the value found in Lines.Text, the area allocated for storage of the textual data of the Memo.

The result is of type TCaption, a string type for the caption of a control: may be translated

 RealSetText - copies Value into Lines.Text (overriding inherited method) TControl.RealSetText Returns a False result The CachedText of type TCaption that is being fetched SetAlignment - right or left justified, or centered SetLines - specify the text strings to occupy Lines SetWantReturns - sets a boolean flag showing that Return characters are to be included in the edit strings SetWantTabs - sets a boolean flag to show that the use of tabs in the edit string is required SetWordWrap - speifies the value of the WordWrap property SetScrollBars - specifies the style of the scroll bars Loaded calls inherited method then sets the ScrollBar and WordWrap properties

The Loaded method is called when a component has finished loading; the various ancestor classes copy properties from client and parent classes into the newly loaded component, and notify any child components of changes that have been made

 TComponent.Loaded TWinControl.Loaded WordWrapIsStored - returns True if the WordWrap flag is stored The result of a test to see whether the property WordWrap has been stored GetControlClassDefaultSize - makes its own defaults, overriding inherited method TControl.GetControlClassDefaultSize Returns the default size, stored as a TPoint

The various ancestor methods first create the object, then initialise sizes, styles, fonts and positions of subsidiary objects

 TWinControl.Create TCustomEdit.Create Create - constructor for TCustomMemo: calls inherited Create then initialises some variables, creates the stringlist and creates scrollbars

The ancestor destructor removes the resources that have been used, in a systematic and orderly way

 TWinControl.Destroy Destroy - destructor for TCustomMemo: frees stringlist and scrollbars then calls inherited Destroy Append - procedure for adding a text string to the Memo Alignment - whether text is centered, left- or right-justified Lines : an array of strings (single lines of characters) which contains the text held or being entered in the Memo Lines : an array of strings (representing single lines of characters) which contains the textual material held or being entered in the Memo. The array is zero-indexed, ie the strings are numbered [0..numLines-1] The horizontal scroll bar for this memo The Vertical scroll bar for this memo Whether the Memo has ScrollBars - none, horizontal or vertical or both, or automatically placed if needed Whether Return characters are required to be included in the memo Whether Tab characters are required to be retained in the Memo Is WordWrap enabled, allowing long words to be carried on to the next line? Word Wrap: a logical flag to show whether or not word-wrap is enabled, ie if a word is close to the end of a line and is going to be too long for the line, it is wrapped down to the next line TEdit - an Edit Box: for entry or display of a single line of text.

If True, indicates that the edit control has just performed an AutoSelect operation so that subsequent mouse-clicks and keystrokes proceed normally without selecting the text.

False is set when the edit control loses focus.

// standard properties, which should be supported by all descendants

The (default) action to be associated with this control

Can either read the action already associated with the control (GetAction), or write an action to be associated (SetAction)

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

// standard properties, which should be supported by all descendants

AutoSize permits the size of a control to be adjusted automatically, for example a button can become bigger or smaller to accommodate a longer or shorter caption.

Reads logical (boolean) flag to see whether auto-sizing is to be operated, or writes the flag to say it should be done. Default is false, ie no auto-sizing

 Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

// standard properties, which should be supported by all descendants

Reads the value for colour, or stores the value, and sets a flag if the colour is stored.

The default colour is the same as the window in which the control is located.

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

Indicates how text is displayed in a text editing control in the following ways:

  • Normal case letters
  • Upper case letters
  • Lower case letters

The rules can, of course, be overridden by use of the shift key.

// standard properties, which should be supported by all descendants

Whether the control is Enabled. If not, it usually appears 'greyed-out'

Reads a flag to see whether the control is enabled, or stores a new value. If stored, sets a flag to say so.

// standard properties, which should be supported by all descendants

Reads a flag to see what font should be used, or sets a flag to store it. If stored, sets a flag to say so

The properties of Font are defined in the parent class TFont

// standard properties, which should be supported by all descendants

Reads or Writes flag if bounds are changed

// standard properties, which should be supported by all descendants

This is often the default action for many controls, and is often the ONLY action specified by the programmer. The action can be spcified by the user, either by typing explicit code into the implementation section for this control, or by selecting an action from a pre-supplied ActionList

Reads or writes a flag if a mouse click is detected, and sets a flag if a value is stored.

Double-clicking is much more common in a Windows environment than in Unix or Linux, where single-clicking is the default method for selecting an object. However, in all environments there could be valid use for a double-click, and a method should be supplied if appropriate.

OnKeyDown - event handler for instance when key is down while control has focus

Differs from OnKeyPress in that the key may have already been down when the control received focus; with OnKeyPress the key needs to become pressed while the control has focus.

OnKeyPress - event controller for a key being pressed while the control has focus

Differs from OnKeyDown in that the key needs to become pressed while the control has focus; with OnKeyDown the key may have already been down when the control received focus.

OnKeyUp - event handler for instance when a key is up (not pressed) while the control has focus

The key may already have been up when the control received focus, or a pressed key may become released during the time the control has focus.

 // standard properties, which should be supported by all descendants
Reads or Writes flag if control is re-sized.

PasswordChar : the character which appears in the Edit box replacing and masking the actual character typed.

Typically used in password input, to prevent the typed characters from being seen by passers-by or casual observers (or even malicious observers!)

 // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu // standard properties, which should be supported by all descendants
Reads flag or writes one to determine if a hint is to be shown when mouse hovers over this control. If value is stored, a storage flag is set. Display of the actual hint is controlled by OnShowHint

Reads or writes boolean flag; default is False

Use the TabStop to allow or disallow access to the control using the Tab key.

If TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't use the Tab key to move to the control.

 Reads or writes information in flag; default is -1 Text : the character string contained in the Edit Box 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility. TMemo - a box for entry or display of multiple lines of text

TMemo - a box for entry or display of multiple lines of text.

The textual data is held as an array of strings in Lines, where it can be edited

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

// standard properties, which should be supported by all descendants

Reads the value for colour, or stores the value, and sets a flag if the colour is stored.

The default colour is the same as the window in which the control is located.

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

// standard properties, which should be supported by all descendants

Whether the control is Enabled. If not, it usually appears 'greyed-out'

Reads a flag to see whether the control is enabled, or stores a new value. If stored, sets a flag to say so.

// standard properties, which should be supported by all descendants

Reads a flag to see what font should be used, or sets a flag to store it. If stored, sets a flag to say so

The properties of Font are defined in the parent class TFont

Lines : an array of strings (representing single lines of characters) which contains the textual material held or being entered in the Memo. The array is zero-indexed, ie the strings are numbered [0..numLines-1]

// standard properties, which should be supported by all descendants

This is often the default action for many controls, and is often the ONLY action specified by the programmer. The action can be spcified by the user, either by typing explicit code into the implementation section for this control, or by selecting an action from a pre-supplied ActionList

Reads or writes a flag if a mouse click is detected, and sets a flag if a value is stored.

Double-clicking is much more common in a Windows environment than in Unix or Linux, where single-clicking is the default method for selecting an object. However, in all environments there could be valid use for a double-click, and a method should be supplied if appropriate.

OnKeyDown - event handler for instance when key is down while control has focus

Differs from OnKeyPress in that the key may have already been down when the control received focus; with OnKeyPress the key needs to become pressed while the control has focus.

OnKeyPress - event controller for a key being pressed while the control has focus

Differs from OnKeyDown in that the key needs to become pressed while the control has focus; with OnKeyDown the key may have already been down when the control received focus.

OnKeyUp - event handler for instance when a key is up (not pressed) while the control has focus

The key may already have been up when the control received focus, or a pressed key may become released during the time the control has focus.

 // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu Reads or writes information in flag; default is -1

Reads or writes boolean flag; default is False

Use the TabStop to allow or disallow access to the control using the Tab key.

If TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't use the Tab key to move to the control.

 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility. Word Wrap: a logical flag to show whether or not word-wrap is enabled, ie if a word is close to the end of a line and is going to be too long for the line, it is wrapped down to the next line TStaticBorderStyle - enumerated type for border of static text: none, single or sunken TCustomStaticText : the base class for Static Text GetLabelText - returns text string for label RealSetText - calls inherited method then adjusts size TControl.RealSetText SetFocusControl - specifies which control has focus SetShowAccelChar - sets boolean flag to determine whether accelerator characters are to be shown GetControlClassDefaultSize returns its own defaults, overriding inherited values TControl.GetControlClassDefaultSize TWinControl.Create Create - constructor for TCustomStaticText: calls inherited Create the initialises style, alignment and bounds Alignment - whether text is centered, left- or right-justified FocusControl - the control that currently receives focus ShowAccelChar - underline the character in the static text that acts as an accelerator with a shortcut key

ShowAccelChar - underline the character in the static text that acts as an accelerator with a shortcut key

Boolean property - default True

 TStaticText : a box to display a Constant Text String

TStaticText : a box to display a Constant Text String

Use this control to display a statement or comment that is not likely to change very often, or is not usually responsive to user actions

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

// standard properties, which should be supported by all descendants

AutoSize permits the size of a control to be adjusted automatically, for example a button can become bigger or smaller to accommodate a longer or shorter caption.

Reads logical (boolean) flag to see whether auto-sizing is to be operated, or writes the flag to say it should be done. Default is false, ie no auto-sizing

 Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

Gets caption as a text-string (GetText), or stores the new caption (SetText). Shows flag if caption is stored (IsCaptionStored).

By default, the Caption appears the same as the control Name in the Object Inspector, and the developer needs to set it explicitly to some new text.

The VCL implementation relies on the virtual Get/SetTextBuf to exchange text between widgets and VCL. This means a lot of (unnecesary) text copies.

The LCL uses strings for exchanging text (more efficient). To maintain VCL compatibility, the virtual RealGet/SetText is introduced. These functions interface with the LCLInterface.

The default Get/SetTextBuf implementation calls the RealGet/SetText. As long as the Get/SetTextBuf isn't overridden Get/SetText calls RealGet/SetText to avoid PChar copying.

To keep things optimal, LCL implementations should always override RealGet/SetText. Get/SetTextBuf is only kept for compatibility.

// standard properties, which should be supported by all descendants

Reads the value for colour, or stores the value, and sets a flag if the colour is stored.

The default colour is the same as the window in which the control is located.

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

 On Click - Action to be taken when the mouse button is clicked with the cursor over this control. User-defined Procedure On Double-click - Action to be taken when the mouse button is double-clicked while the cursor is over the control. User-defined Procedure On Mouse Down - Action to be taken when the mouse button is down while the cursor is over this control. User-defined Procedure On Mouse Entry - Action to be taken when the mouse cursor enters the bounds of this control. User-defined Procedure On Mouse Leaving - Action to be taken when the mouse cursor leaves the boundaries of this control. User-defined Procedure. On Mouse Movement - Action to be taken if the mouse cursor moves within the bounds of this control. User-defined Procedure On Mouse Up - Action to be taken if the mouse button is up while the cursor is over this control. On Resize - Action to be taken when the control is resized. Might include re-alignment of text or selection of a different font size etc. User-defined Procedure Visible - determines whether or not the control can be seen TButtonControl : ancestor class for several Button (including Radio Button) and Check Box classes fLastCheckedOnChange - local boolean variable to show whether the button was checked at the last OnChange event GetChecked - returns True if the button is checked SetChecked - specifies whether or not the button is checked DoOnChange - perform the code of the OnChange event

Click - the procedure which allows programmatic simulation of a mouse click, and thus activation of the Action associated with the OnClick event

Loaded is called by the streaming system when a root component was completely read from a stream and all properties and references to other objects have been resolved by the streaming system. Descendents of TComponent should override this method to do some additional processing of properties after all published properties have been set from values obtained from the stream.

Application programmers should never call Loaded directly, this is done automatically by the streaming system.

Checked - whether this button has been checked, which signifies selection ClicksDisabled - if True, clicks are disabled for this button control UseOnChange - if true, this control is to be used if any change occurs OnChange - event handler for any change in properties of the control TWinControl.Create Create - constructor for TButtonControl: calls inherited Create then initialises style TButtonActionLink - provides a link between a button and its corresponding action

TButtonActionLink - provides a link between a button and its corresponding action

This class provides very few properties of its own, but inherits a lot from its ancestors, TWinControlActionLink, TControlActionLink, TActionLink and TBasicActionLink

FClientButton - local variable showing the button to which this action applies AssignClient calls inherited method then sets up client as a ButtonControl TBasicActionLink.AssignClient SetChecked - writes Checked status of button to local variable TActionLink.SetChecked TButtonActionLinkClass - class of TButtonActionLink TCustomButton - the base class for TButton and TBitBtn

Click - the procedure which allows programmatic simulation of a mouse click, and thus activation of the Action associated with the OnClick event

TControl.Click Click - checks if the parent form has a Modal Result, then calls inherited method CreateWnd calls inherited method and sets default Widget Set TWinControl.CreateWnd GetControlClassDefaultSize returns its own defaults, overriding the inherited values TControl.GetControlClassDefaultSize WSSetDefault - writes the default widget set to local variable WSSetText - writes the text name of the widget set to a local variable If you drop a component on the form editor you don´t need to add code to explicitly create it. The component is automatically created together with the the form, and destroyed when the form is destroyed. TWinControl.Create Create - constructor for TCustomButton: calls inherited Create then initialises style, colour, bounds, alignment and various other properties TControl.ExecuteDefaultAction ExecuteDefaultAction if the control is active or default, executes the Click action TControl.ExecuteCancelAction ExecuteCancelAction if this is a Cancel button, executes the Click action Is this control Active - has it got Focus; is the mouse over it? Is this the Default button? (default setting is False)

Defines if a button is the Default on a form. That is, pressing ENTER will execute its onClick method, whether the control has focus or not!

 Determines whether the button closes its modal parent form. The default value is mrNone. Is this the Cancel button? (default setting is False)

Setting this property to true, will have the effect that when the user hits ESC this button is Clicked, even if the button does not have focus. Usually the Button which reacts to ESC sets the ModalResult of the form to mrCancel.

 If you want to programmatically Click on a button you can call its Click method. This will have the same effect as a user clicking on the button.

// standard properties, which should be supported by all descendants

The (default) action to be associated with this control

Can either read the action already associated with the control (GetAction), or write an action to be associated (SetAction)

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

// standard properties, which should be supported by all descendants

AutoSize permits the size of a control to be adjusted automatically, for example a button can become bigger or smaller to accommodate a longer or shorter caption.

Reads logical (boolean) flag to see whether auto-sizing is to be operated, or writes the flag to say it should be done. Default is false, ie no auto-sizing

 Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

Setting this property to true, will have the effect that when the user hits ESC this button is Clicked, even if the button does not have focus. Usually the Button which reacts to ESC sets the ModalResult of the form to mrCancel.

Gets caption as a text-string (GetText), or stores the new caption (SetText). Shows flag if caption is stored (IsCaptionStored).

By default, the Caption appears the same as the control Name in the Object Inspector, and the developer needs to set it explicitly to some new text.

The VCL implementation relies on the virtual Get/SetTextBuf to exchange text between widgets and VCL. This means a lot of (unnecesary) text copies.

The LCL uses strings for exchanging text (more efficient). To maintain VCL compatibility, the virtual RealGet/SetText is introduced. These functions interface with the LCLInterface.

The default Get/SetTextBuf implementation calls the RealGet/SetText. As long as the Get/SetTextBuf isn't overridden Get/SetText calls RealGet/SetText to avoid PChar copying.

To keep things optimal, LCL implementations should always override RealGet/SetText. Get/SetTextBuf is only kept for compatibility.

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

Defines if a button is the Default on a form. That is, pressing ENTER will execute its onClick method, whether the control has focus or not!

// standard properties, which should be supported by all descendants

Whether the control is Enabled. If not, it usually appears 'greyed-out'

Reads a flag to see whether the control is enabled, or stores a new value. If stored, sets a flag to say so.

// standard properties, which should be supported by all descendants

Reads a flag to see what font should be used, or sets a flag to store it. If stored, sets a flag to say so

The properties of Font are defined in the parent class TFont

// standard properties, which should be supported by all descendants

Reads or Writes flag if bounds are changed

// standard properties, which should be supported by all descendants

This is often the default action for many controls, and is often the ONLY action specified by the programmer. The action can be spcified by the user, either by typing explicit code into the implementation section for this control, or by selecting an action from a pre-supplied ActionList

Reads or writes a flag if a mouse click is detected, and sets a flag if a value is stored.

OnKeyDown - event handler for instance when key is down while control has focus

Differs from OnKeyPress in that the key may have already been down when the control received focus; with OnKeyPress the key needs to become pressed while the control has focus.

OnKeyPress - event controller for a key being pressed while the control has focus

Differs from OnKeyDown in that the key needs to become pressed while the control has focus; with OnKeyDown the key may have already been down when the control received focus.

OnKeyUp - event handler for instance when a key is up (not pressed) while the control has focus

The key may already have been up when the control received focus, or a pressed key may become released during the time the control has focus.

 // standard properties, which should be supported by all descendants
Reads or Writes flag if control is re-sized. // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu // standard properties, which should be supported by all descendants
Reads flag or writes one to determine if a hint is to be shown when mouse hovers over this control. If value is stored, a storage flag is set. Display of the actual hint is controlled by OnShowHint Reads or writes information in flag; default is -1 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility. TCheckBoxState - enumerated type for state of checkbox Check Box State: an enumerated list of constants defining the possible states of a Check Box - Unchecked, Checked or Greyed The check box has no check mark, indicating that the user has not selected the option. The check box has a check mark in it, indicating that the user has selected the option. The check box has a check mark in it, but it is grayed. TCustomCheckBox is the ancestor of all check-box components.

TCustomCheckBox : The base (abstract) class from which the TCheckBox is derived.

Check boxes present the user with options that can be selected (checked) or deselected (unchecked).

Click - the procedure which allows programmatic simulation of a mouse click, and thus activation of the Action associated with the OnClick event

RetrieveState - returns the value for check box state InitializeWnd calls inherited method and applies any changes TWinControl.InitializeWnd Toggle - method to alternate between checked and unchecked states on successive activations ApplyChanges - method for applying specified changes GetControlClassDefaultSize - returns its own defaults, overriding the inherited values TControl.GetControlClassDefaultSize Loaded - sends the State of the box to the interface before calling inherited method TComponent.Loaded TWinControl.Loaded Create - constructor for TCustomCheckBox: calls inherited Create then initialises style, and state, bounds, tabstop and autosize TWinControl.Create Determines whether the check box can be in a "grayed" state.

If AllowGrayed is set to True, the check box has three possible states: checked, unchecked and grayed. If AllowGrayed is set to False, the check box has only two possible states: checked and unchecked.

 Indicates whether the check box is checked (selected), unchecked (deselected) or grayed.

See TCheckBoxState for possible values of State.

 Use the TabStop to allow or disallow access to the control using the Tab key. If the TabStop is True, the control is in the tab order. If TabStop is False, the control is not in the tab order and the user can't press the Tab key to move to the control. TCheckBox - a small box which can contain a check mark to indicate that it has been selected by a mouse click

TCheckBox : a small box which can contain a check mark to indicate that it has been selected by a mouse click. May be associated with a Caption that describes its function.

 TToggle Box : a labelled box capable of being checked or unchecked

TToggle Box : a labelled box capable of being checked (when it becomes recessed) or unchecked (when it is raised).

The Application Programmer is responsible for ensuring that the OnClick event handler recognises the State of the box, takes the appropriate Action and places the State into the next appropriate value

 TCustomCheckBox.Create Create - constructor for TToggleBox: calls inherited Create then initialises style and makes autosize False

If AllowGrayed is set to True, the check box has three possible states: checked, unchecked and grayed. If AllowGrayed is set to False, the check box has only two possible states: checked and unchecked.

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

// standard properties, which should be supported by all descendants

AutoSize permits the size of a control to be adjusted automatically, for example a button can become bigger or smaller to accommodate a longer or shorter caption.

Reads logical (boolean) flag to see whether auto-sizing is to be operated, or writes the flag to say it should be done. Default is false, ie no auto-sizing

 TRadioButton : a button that works with other Radio Buttons in a mutually exclusive way - if one button is selected, none of the others in the group can be selected

TRadioButton : a button that works in conjunction with other Radio Buttons in a mutually exclusive manner - if one button of a group is selected, none of the others in that group can be selected.

The Application Programmer is responsible for ensuring that the OnClick event handler for each button has a unique Action, and that the Actions of the other (deselected and therefore inactive) buttons are turned off.

TRadioGroup behaves differently from a group of TRadioButton controls placed arbitrarily around a form.

In the case of TRadioButton, the mutual exclusivity is a feature that applies to any RadioButton anywhere in the Form, and the RadioButtons can be rearranged in any order or placed anywhere within the containing Form, while in TRadioGroup the exclusivity applies only to buttons within the Group, which are ordered strictly according to their ItemIndex within the Items stringlist.

TRadioButton is an entity in itself, with a number of additional properties, whereas the buttons within TRadioGroup are not separate entities, but rather are simply entries in a list of strings, each of which is associated with the on-screen image of a RadioButton.

The example shows the difference between the use of TRadioButton and TRadioGroup

TRadioGroup Create - constructor for TRadioButton: calls inherited Create then initialises style TCustomCheckBox.Create TCustomLabel : the base type from which TLabel is derived. TCustomLabel : the base type from which TLabel is derived. CanTab - always set to False, as you can't tab to a label TControl.CanTab DoMeasureTextPosition - method for measuring position of text; shows position of top and left edges HasMultiLine - returns True if label has multiple lines DoAutoSize GetControlClassDefaultSize returns its own defaults, overriding inherited values TControl.GetControlClassDefaultSize WMActivate - LCL message to activate control Notification calls inherited method and adjusts focus, if required TControl.Notification GetShowAccelChar - returns True if accelerator characters aer to be shown GetAlignment - returns the value of alignment required GetLabelText - returns the string for text of the label GetTransparent - returns True if the control is to be transparent SetAlignment - specifies the sort of alignment (left or right justified or centered) SetFocusControl - specifies which control has focus SetLayout - specifies text layout SetShowAccelChar - specifies whether accelerator characters are to be shown SetTransparent - specifies whether the control is to be transparent SetWordWrap - specifies whether WordWrap is to be used

Loaded is called by the streaming system when a root component was completely read from a stream and all properties and references to other objects have been resolved by the streaming system. Descendents of TComponent should override this method to do some additional processing of properties after all published properties have been set from values obtained from the stream.

Application programmers should never call Loaded directly, this is done automatically by the streaming system.

TControl.Loaded Loaded calls inherited method and adjusts size Alignment - whether text is centered, left- or right-justified FocusControl - which control has focus Layout - How the Text is to be laid out in the text rectangle: at the Bottom, Centre or Top ShowAccelChar - underline the character in the label that acts as an accelerator with a shortcut key

ShowAccelChar - underline the character in the label that acts as an accelerator with a shortcut key

Boolean property - default True

 Transparent - whether the viewer can see through the control. Default True WordWrap - whether a word is to be wrapped to the next line if the text is about to become too long for the width available

WordWrap - whether a word is to be wrapped to the next line if the text is about to become too long for the width available

Boolean property, default False

 OptimalFill - boolean. If True, font size is adjusted for optimal fill of available space TGraphicControl.Create Create - constructor for TCustomLabel: calls inherited Create then initialises style, bounds, colour and some other properties Calculate the height of the font needed to fit the available space, given the MaxWidth and MaxHeight constraints If True, attempts to adjust font for an optimal fill of the space available Virtual Paint method called in response to paint requests received by the parent control.

// standard properties, which should be supported by all descendants

AutoSize permits the size of a control to be adjusted automatically, for example a button can become bigger or smaller to accommodate a longer or shorter caption.

Reads logical (boolean) flag to see whether auto-sizing is to be operated, or writes the flag to say it should be done. Default is false, ie no auto-sizing

// standard properties, which should be supported by all descendants

Reads the value for colour, or stores the value, and sets a flag if the colour is stored.

The default colour is the same as the window in which the control is located.

 TLabel : a brief text label to be placed in the Form near any object that needs to be identified.

// standard properties, which should be supported by all descendants

Either reads a flag containing alignment instructions (FAlign) or writes alignment instructions (SetAlign)

May have no alignment, may have custom or client alignment, or can be aligned to top, bottom, left or right

// standard properties, which should be supported by all descendants

Determines how the control is to be anchored to its client or parent conrol

Either reads a flag containing the set of anchors to be used, or writes a set of anchors. If they have been written, this is indicated in IsAnchorsStored

// standard properties, which should be supported by all descendants

AutoSize permits the size of a control to be adjusted automatically, for example a button can become bigger or smaller to accommodate a longer or shorter caption.

Reads logical (boolean) flag to see whether auto-sizing is to be operated, or writes the flag to say it should be done. Default is false, ie no auto-sizing

 Allows Languages such as Arabic and Hebrew to be used

// standard properties, which should be supported by all descendants

Determines the border spacing for this control

Reads flag to find stored spacing values required for the border of the control, or writes the flag to set the spacing.

The properties are defined in the parent class TControlBorderSpacing

Gets caption as a text-string (GetText), or stores the new caption (SetText). Shows flag if caption is stored (IsCaptionStored).

By default, the Caption appears the same as the control Name in the Object Inspector, and the developer needs to set it explicitly to some new text.

The VCL implementation relies on the virtual Get/SetTextBuf to exchange text between widgets and VCL. This means a lot of (unnecesary) text copies.

The LCL uses strings for exchanging text (more efficient). To maintain VCL compatibility, the virtual RealGet/SetText is introduced. These functions interface with the LCLInterface.

The default Get/SetTextBuf implementation calls the RealGet/SetText. As long as the Get/SetTextBuf isn't overridden Get/SetText calls RealGet/SetText to avoid PChar copying.

To keep things optimal, LCL implementations should always override RealGet/SetText. Get/SetTextBuf is only kept for compatibility.

// standard properties, which should be supported by all descendants

Reads the value for colour, or stores the value, and sets a flag if the colour is stored.

The default colour is the same as the window in which the control is located.

// standard properties, which should be supported by all descendants

Determine Constraints (max and min height and width) for this control; reads the size constraints or stores new ones.

// standard properties, which should be supported by all descendants

Whether the control is Enabled. If not, it usually appears 'greyed-out'

Reads a flag to see whether the control is enabled, or stores a new value. If stored, sets a flag to say so.

// standard properties, which should be supported by all descendants

Reads a flag to see what font should be used, or sets a flag to store it. If stored, sets a flag to say so

The properties of Font are defined in the parent class TFont

Layout - How the Text is to be laid out in the text rectangle: at the Bottom, Centre or Top // standard properties, which should be supported by all descendants
Reads the details of the pop-up menu, or stores them.
Properties are defined in the parent class TPopupMenu

ShowAccelChar - underline the character in the label that acts as an accelerator with a shortcut key

Boolean property - default True

 // standard properties, which should be supported by all descendants
Reads flag or writes one to determine if a hint is to be shown when mouse hovers over this control. If value is stored, a storage flag is set. Display of the actual hint is controlled by OnShowHint 
The Visible property represents the ability to see a visual control. 
          If Visible is True the control is shown, otherwise it is hidden.
          Calling Show sets, among others, Visible to True.
          Setting Visible to False is equivalent to calling Hide method.
The Visible property does not depend on control's parent visibility. Use IsVisible method to consider this and get real visibility.

WordWrap - whether a word is to be wrapped to the next line if the text is about to become too long for the width available

Boolean property, default False

// standard properties, which should be supported by all descendants

This is often the default action for many controls, and is often the ONLY action specified by the programmer. The action can be spcified by the user, either by typing explicit code into the implementation section for this control, or by selecting an action from a pre-supplied ActionList

Reads or writes a flag if a mouse click is detected, and sets a flag if a value is stored.

Double-clicking is much more common in a Windows environment than in Unix or Linux, where single-clicking is the default method for selecting an object. However, in all environments there could be valid use for a double-click, and a method should be supplied if appropriate.

// standard properties, which should be supported by all descendants

Reads or Writes flag if bounds are changed

 // standard properties, which should be supported by all descendants
Reads or Writes flag if control is re-sized. How to use StdCtrls, ComCtrls or ExtCtrls

The Units StdCtrls, ComCtrls and ExtCtrls contain definitions and descriptions of many of the most commonly used controls for constructing Forms and other Objects in Lazarus Applications.

Many of the final target controls that the application developer wants to use, such as TButton, TMemo, TScrollBar etc, have a corresponding ancestor class such as TCustomButton, TCustomMemo or TCustomScrollBar. Several of the properties and methods relevant to the final target control are defined (and explained) more fully in the TCustomXXX class, and are inherited by the final target control.

If you drop a component on the form editor you don't need to add code explicitly to create it. The component is automatically created by the IDE together with the form, and destroyed when the form is destroyed.

However, if you create the component yourself by code don't forget to free it when it is no longer needed.

If you place a component on the Form Designer and look at the Object Inspector, you can observe the properties change as you move the component around.

For example, if you place a button (TButton) on the form, click on it to select it, then move it around the form with the mouse, you can watch the values of Top and Left change in the Object Inspector to reflect the new position. If you use the object's re-sizing bars to adjust its size, you can watch the Height and Width properties change as well.

On the other hand, by using the Object Inspector, you can select the value associated with a property such as height, and type in a new value; you can watch the size of the object on the form change to reflect the new value.

You can also explicitly change the properties of the object in code by typing (in the appropriate Implementation section of the Source editor), for example

Form1.Button1.Height := 48;

If you type this new value into the Source Editor and then look back at the Form Designer, you will see that the button on the Form has taken the new size. The new value will also be shown in the Object Inspector.

In summary, there are usually about three different ways to determine each property of an object:

  • by using the mouse,
  • by setting the values in the Object Inspector,
  • or explicitly by writing code.

The components defined in these Units have several properties that are common to most of them, and other properties that are specific to the individual components. We shall describe the most common ones here. Unusual or control-specific properties will be described for the individual controls.

Additional Help can always be obtained by selecting a property or keyword, in either the Object Inspector or the Source Editor, and pressing F1. You will be taken by your Help browser to the appropriate page in the documentation.

If the description of a property on that page is insufficient, you can navigate to the corresponding description in the ancestor classes, by selecting the links in the Inheritance listing or by selecting the ancestor Type in the declaration of the object.

Constructors such as Create allocate memory and system resources needed by the object. They also call the constructor of any sub-objects present in the class.

Destructors: remove the object and de-allocate memory and other resources. If you call Destroy for an object which hasn't being initialized yet it will generate an error. Always use the Free method to deallocate objects, because it checks whether an object's value is nil before invoking Destroy.

Take the following precautions when creating your own Destroy method:

  • Declare Destroy with the override directive, because it is a virtual method.
  • Always call 'inherited Destroy;' as the last thing on the destructor code.
  • Be aware that an exception may be raised on the constructor in case there is not enought memory to create an object, or something else goes wrong. If the exception is not handled inside the constructor, the object will be only partially built. In this case Destroy will be called when you weren't expecting it, so your destructor must check if the resources were really allocated before disposing of them.
  • Remember to call Free for all objects created on the constructor.
Some commonly listed properties
Property Meaning
Action The main action or event associated with the object. For example selecting an 'Exit' Button might cause the 'Close' action
Align Defines the way in which an object is to be lined up with the parent object. Possible values are alTop (placed at the top and using the full available width), alBottom, alLeft (placed at the left and using the full available height), alRight. alNone (place anywhere on parent control) or alClient (takes all available space next to controls aligned to top, bottom, left or right)
Anchor Used to keep a control a certain distance from the defined edges of a parent control, when the parent is resized. For example [akBottom, akRight] will keep the control a fixed distance from the bottom right corner.
AutoSelect When True, an editing control will select all its text when it receives focus or when the Enter key is pressed.
AutoSelected True indicate that the edit or combobox control has just performed an AutoSelect operation so that subsequent mouse-clicks and keystrokes proceed normally without selecting the text.
BorderSpacing The space around the edge between an Anchored control and its parent.
Caption The text that is displayed on or near the control; it should preferably give some clue as to the function of the control, or an instruction such as 'Close' or 'Execute'. By default Caption is set to be the same as the 'Name' property, and the application programmer should substitute meaningful text instead of the default values.
CharCase Indicates how text is displayed in a text editing control: Normal (retaining the case of the letters typed by the user), converted to uppercase, or converted to lowercase
Constraints Sets the minimum and maximum sizes for a control. If a control is resized the new dimensions are always within the ranges given here. You should take care when setting these options that they do not conflict with the Anchors and Align settings.
Color The Colour to be used to draw the control or to write the text it contains.
Enabled A Boolean property to determine whether or not a control is capable of being selected and performing an action. If it is not Enabled, it is often Grayed out on the Form.
Font The Font to be used for writing the text associated with the control - either the caption or label, or the text-strings contained within the control. The entry on the Object Inspector usually has a (+) box on the left, and selecting this box reveals further options such as character set, colour and size.
Hint A short piece of informative pop-up text that appears if the mouse-cursor hovers over the control.
Items The list of 'Things' that the object contains, such as a group of images, a series of lines of text, a number of actions in an actionlist, etc
Lines An array of strings, containing the textual data in controls with more than a single line of data, such as an Edit-Box or a Combo-Box. The array is zero-indexed, ie the lines are numbered [0..numLines-1]
Name The identifier by which the control is known in the program. The IDE gives it a default name based on the underlying type, for example successive instances of TBitButton would be named Form1.BitBitton1 and Form1.BitButton2; it is up to the application programmer to give them more meaningful names such as ExitButton or OKButton. By default the Name of the control is applied to the Caption for the control, but the text of the Caption may be changed separately.
PopUpMenu A window containing context-sensitive menu information that pops up when the right mouse button is clicked on the object.
Position (or Top, Left) Determines where the control is located on the parent form or window
ReadOnly Boolean property which, if True, signifies that the contents of the control can be read by the user or the calling routine, but cannot be written or changed.
ShowHint Allows a small window containing a context-sensitive Help or other description to be displayed when the mouse cursor 'hovers' over the control.
Size (or Height and Width) The dimensions of the control
Style The options available for Style depend upon the sort of Control being considered: for instance the Style may be defined by TFormStyle, TBorderStyle, TButtonStyle etc.
TabOrder Integer defining where in the sequence of tabs on the Form this control is to lie
TabStop Boolean property which if True places this control in the sequence of objects that the user can reach by successively pressing the Tab key
Text The String of Text that represents the actual data that this control contains. Applies particularly to Text, Memo and StringList types of object. Most of the editing operations (such as Select, Clear, Cut, Copy) are performed in this part of the object, which holds the actual string being edited. If the control contains more than a single line of text, for example TMemo or TComboBox, then the textual elements are arranged as an array of strings (zero-indexed, ie numbered from [0..numLines-1]) in Lines.
Visible If true, the object can be seen on the Form; if False, object is hidden
WordWrap Logical flag to show whether or not word-wrap is enabled, ie if a word comes close to the end of a line and is going to be too long for the line, it is wrapped down to the next line.

Many actions are commonly listed in the 'Events' tab of the Object Inspector. If you select an entry in the list, a ComboBox appears with a DropDown list showing any actions that have aleady been defined, and allowing you to choose one to be associated with this event. Alternatively you can select the ellipsis (three dots ...) and you will be taken to an area of the Source Editor where you can begin typing your own action instructions for the selected event.

While a large number of events is available for any given control, in practice it is only necessary to populate a few of them. For most controls, it is sufficient to provide coding for 'OnClick'; for more complex controls it may be necessary also to provide for 'OnEntry' (when the mouse cursor enters the Control and gives it focus) and 'OnExit' (when the mouse cursor leaves the Control; or you may need to write an event handler for 'OnChange' or 'OnScroll', depending on the nature of the particular control with which you are dealing.

The pop-up menu that appears when you right-click an object in the Form Designer has, as its first item: 'Create default event' and selecting this option will have the same effect as selecting the ellipsis in the Object Inspector for the default event, usually OnClick: you are taken to the Implementation area of the Source Editor where you can type the code for the event handler.

A common strategy in Object-Oriented programming is to provide an ActionList with the facility for entering, removing or editing a number of pre-defined actions from which the most appropriate can be selected to use in any particular instance.

Some commonly listed Actions
Action Meaning
OnChange Action to be taken if any change is detected (eg mouse move, mouse click, key press, edit text, alter picture, etc)
OnClick Action to be taken when the (left) mouse button is clicked. This is usually the main or default action of the control; for example clicking on a button or checkbox initiates the action associated with the checkbox. It may alternatively initate a process of selection, for instance in a TextBox or Memo, or signal the beginning of painting with a Pen or Brush.
Click A method to emulate in code the effect of clicking on a control. This method is most often found in Button-type controls (TButton, TBitBtn, TSpeedButton etc). A procedure can be written that calls the same code as the OnClick action. This facility can be particularly useful if the activation of one control by clicking causes a cascade of other controls to be activated, and the Click method can be used to initiate the action rather than having the user explicitly click on a lot of controls.
OnDragDrop Action to be taken during Drag-Drop manoeuvres, ie when the mouse is used to 'capture' an item or some text etc and move it around the screen to a new location.
OnEntry Action to be taken when the mouse cursor enters the area occupied by the object, usually transfering focus to that object. This might include changes in the appearance of the object such as highlighting or raising the border.
OnExit Action to be taken when the mouse moves out of the area of the object, usually transferring focus out of the object.
OnKeyPress Action to be taken for any key-press. Subtly different from OnKeyDown, which simply responds to a key being down, whether or not it was already down when focus was given to this control. OnKeyPress requires that a key becomes pressed while focus is in this control.
OnKeyDown Action to be taken if a key is down while focus is in this control. Subtly different from OnKeyPress - for example the key might already have been down when focus entered this control, whereas OnKeyPress requires the key to become pressed while focus is in the control.
On Key Up Action to be taken if a key is up (ie not pressed) while focus is in this control.
OnMouseMove On Mouse Down - Action to be taken if the mouse cursor moves while focus is in this control.
OnMouseDown Action to be taken if the mouse button is down while focus is in this control.
OnMouseUp Action to be taken if the mouse button is up while the cursor is over this control. Implies that the mouse button was previously down and has been released. The case where the cursor enters the control but the mouse button has not yet been pressed is covered by OnEntry or OnMouseEnter.
OnResize Action to be taken when the control is resized. Might include re-alignment of text or selection of a different font size etc.

// standard properties, which should be supported by all descendants

AutoSize permits the size of a control to be adjusted automatically, for example a button can become bigger or smaller to accommodate a longer or shorter caption.

Reads logical (boolean) flag to see whether auto-sizing is to be operated, or writes the flag to say it should be done. Default is false, ie no auto-sizing

 AutoSize defaults to True, overriding any previous default TControl.AutoSize SelectAll - select all items in list Undo the last edit action CanUndo - if True, the Undo action is permitted CaretPos - the position of the Caret indicator in the text CalculateStandardItemHeight - returns a calculated value for the standard height of items in th elistbox GetCaretPos - returns the position of the caret or edit cursor GetReadOnly - returns the boolean ReadOnly status SetCaretPos - specifies the position of the caret or edit cursor GetItems - finds the list of items for the dropdown box OnGetItems - event handler for getting list of items for dropdown box GetIndexAtXY - returns the index of an item at the specified coordinates UTF8KeyPress converts character case if required then calls inherited method TWinControl.UTF8KeyPress

The inherited method emulates the pressing of a key, with UTF8 coding. The UTF8 coding should be used where there is the possibility that input/output will occur in any language that requires multiple bytes to represent each character, ie almost all languages except the standard Western European languages.

 Loaded calls inherited method, checks to see whether it is a default or cancel control, sets the default widget set TWinControl.Loaded Click - sets Checked to True then calls inherited Click TControl.Click Alignment - whether text is left- or right-justified, or centered InitializeWnd - initialises the window by creating the borders and outline, then loading up any strings that have already been specified for display

Calls the inherited method which works out the correct bounds, sets style, fonts and colours, performs any pending resize operations

 TWinControl.InitializeWnd FinalizeWnd - getting ready to close down the window: first stores the text strings in a safe place, then frees the storage occupied by them

Calls the inherited method, which prepares to free the handle for this window

 TWinControl.FinalizeWnd Returns the position of the cursor marker or caret HideSelection: hide the selection when control has no focus Allows to turn on the persistent selection. Therefore when control loses focus it still highlights the selected text.