ReadData is a procedure used to read the data for Items in the control from the specified TStream instance.

WriteData is a procedure used write data for the control to the TStream instance.

ClickCheck is a method used to perform actions needed when a value in the control is about to change.

ClickCheck signals the OnClickCheck event handler (when assigned) using the current class instance as the object for the event notification. Use OnClickCheck to implement the actions needed when the control has been changed.

ClickCheck is called when the LM_CHANGED message is handled for the control, and occurs prior to calling the ItemClick method where the OnItemClick event handler is signalled.

ClickCheck is also called from the KeyDown method when the Space key has been pressed while the control has focus. It is called after ItemIndex has been range adjusted (when needed) and the inherited Click method is called. In addition, the value in Checked has already been toggled before the method is called. ClickCheck is not called for the keystroke when the check box item in ItemIndex is not enabled.

ItemClick is a method used to perform actions need when the value for the check box item in AIndex has been changed. AIndex is the ordinal position for the check box in the Items for the control. ItemClick signals the OnItemClick event handler (when assigned) using the current class instance and the value in AIndex as arguments.

ItemClick is called when the LM_CHANGED message is handled for the control, and occurs after the ClickCheck method has been called to signal the OnClickCheck event handler.

ItemClick is also called from the KeyDown method when the Space key has been pressed while the control is focused. It occurs after the value in ItemIndex is range adjusted (if needed) and the inherited Click method has been called. In addition, the value in Checked has already been toggled before the method is called. ItemClick is not called for the key event when the check box item in ItemIndex is not enabled.

KeyDown is an overridden method in TCustomCheckListBox used to handle key down messages for the control. KeyDown ensures that the value for the current check box is toggled when the Space key is pressed while the control has focus.

This includes setting ItemIndex to 0 when it has a value not valid for the Items defined in the control. The inherited Click method is called if ItemIndex is range adjusted. This behavior is Delphi (version 7 at least) compatible.

If the check box at ItemIndex has its ItemEnabled property set to True, the value in Checked is toggled. The ClickCheck and ItemClick methods are called to trigger the corresponding event handlers. The value in Key is set to VK_UNKNOWN when the keystroke has been handled in the method.

The inherited KeyDown method is called to handle other key down events.

FontChanged is an overridden method in TCustomListBox used to perform actions when the Font for the control has been changed. FontChanged calls the inherited method on entry. The value in ItemHeight is updated (at run-time) when the control Style is set to lbStandard.

Create is the overridden constructor for TCustomCheckListBox. It calls the inherited Create method, and sets the component style flag for the control. It also calls the inherited GetCachedDataSize method to determine the storage size needed for each cached item in the control. Create sets the default values for the HeaderBackgroundColor and HeaderColor properties.

CalculateStandardItemHeight is an overridden method used to calculate the height for an item on the check list control.

CalculateStandardItemHeight calls the inherited method on entry to get the height for an item using the Canvas and Font in the class instance. The value is adjusted when needed to the size needed for the SM_CYMENUCHECK system metric. 2 pixels are added to the value as padding, and it is stored in the return value for the method.

CalculateStandardItemHeight is called from the FontChanged method, and occurs when the Font size is changed for the control. It is also called when the LM_MeasureItem is handled in the ancestor class (TCustomListBox).

CalculateStandardItemHeight is used when Style is set to a value other than lbOwnerDrawVariable. Use the OnMeasureItem event handler to calculate the item height when Style is set to lbOwnerDrawVariable.

Toggle is a procedure used to toggle the checked, unchecked, or grayed state for the item at the specified position in Items.

Toggle ensures the value in the AllowGrayed property is respected in the operation. When AllowGrayed is True, the following order is used for toggling to the next available check box state:

• cbUnchecked
• cbChecked
• cbGrayed
• Cycle to cbUnchecked

When AllowGrayed is False, the following order is used for toggling to the next available check box state:

• cbUnchecked
• cbChecked
• Cycle to cbUnchecked

Use Checked to set a specific item to a specified Boolean checked state value. Use State to get or set the check box state as a TCheckBoxState value. Use CheckAll to change the checked state and disposition for all Items in the control.

CheckAll is a procedure used to set the specified values for the State, AllowGrayed, and ItemEnabled properties for all Items in the control. The default value for both aAllowGrayed and aAllowDisabled is True. CheckAll iterates over the entries in the Items property and updates the State property to match the value in the arguments to the method.

Use Checked to set a specific item to a specified Boolean checked state value. Use State to get or set the check box state as a TCheckBoxState value. Use ItemEnabled to get or set the enabled state for a specific entry in Items.

AllowGrayed is a Boolean property which indicates if Items in the control can use the "grayed" (or unselectable) check box State. The default value for the property is False, and indicates that only Checked and Unchecked values can be used in the State property.

Checked is an indexed Boolean property which provides access to the Checked or Unchecked state for Items in the control. The value for the property is True when State contains any value other than cbUnchecked. Setting the value for the property updates State to contain either cbChecked (when True) or cbUnchecked (when False).

Header is an indexed Boolean property which indicates if the specified item is used as a header (instead of a check box) in the control. When the property contains True, the item is rendered as text and does not include any check box behavior.

Reading the value in Header causes the CheckIndex method to be called to validate the value in Index. If a handle has been allocated for the control, the GetHeader method in the widget set class is called to get the value for the property. Otherwise, the cached item data for the control is examined to get the property value.

Setting a new value for the property causes the CheckIndex method to be called to validate the value in Index. If a handle has been allocated for the control, the SendItemHeader method is called to set the value for the property. Otherwise, the cached item data for the control is updated.

HeaderBackgroundColor is a TColor property with the color used to paint the background for a header item on the control. It is used in the widgetset class when a header item is rendered on the control.

The default value for the property is clInfoBk. Changing the value for the property causes the control to be redrawn.

Use HeaderColor to set the font color for header items on the control.

Use the public Header property to identify whether a value in Items is displayed as a non-checkable entry in the list drawn using the colors in HeaderBackgroundColor and HeaderColor.

HeaderColor is a TColor property with the color for the font used to render the text on a Header item. It is used in the widgetset class when a header item is rendered on the control.

The default value for the property is clInfoText. Changing the value for the property causes the control to be redrawn.

Use the HeaderBackgroundColor property to set the background color for a header item on the control.

Use the public Header property to identify whether a value in Items is displayed as a non-checkable entry in the list drawn using the colors in HeaderBackgroundColor and HeaderColor.

ItemEnabled is an indexed Boolean property which provides access to the enabled state for Items in the control. When the property value is True, the item can be selected to change its State or Checked values. When it is False, it behaves as if the check box has been disabled for the item.

Reading the value for the property cause the CheckIndex method to be called to validate the value in Index. If a handle has been allocated for the control, the GetItemEnabled method in the widget set class is called to get the value for the property. Otherwise, the disabled state in cached item data is examined to get the property value.

Setting the value for the property causes the CheckIndex method to be called to validate the value in Index. If a handle has been allocated for the control, the SetItemEnabled method in the widget set class is called to set the value for the property. Otherwise, the disabled state in cached item data is update with the new property value.

Use the Enabled property to indicate whether the check list box control can be updated.

State is an indexed TCheckBoxState property which provides access to the check box state for Items in the control. The TCheckBoxState enumeration value indicates whether the specified item is in a Checked, Unchecked, or Grayed state.

Reading the value in State causes the CheckIndex method to be called to validate the value in AIndex. If a handle has been allocated for the control, the GetState method in the widget set class is called to get the value for the property. Otherwise, the cached item data for the control is examined to get the value for the property.

Setting the value in State causes the CheckIndex method to be called to validate the value in AIndex. If a handle has been allocated for the control, the SendItemState method is called to set the value for the property in the widget set class. Otherwise, the cached item data for the control is updated with the new property value.

Use Checked to get or set the check box state for an item in the control using a Boolean value. Use CheckAll to set the check box state for all Items in the control. Use Toggle to select the next check box state for an item in the control.

OnClickCheck is a TNotifyEvent property with the event handler signalled when the check box state for one of the list items has been changed.

Applications must implement and assign a procedure using the TNotifyEvent signature to respond to the notification. The Sender argument contains the TCheckListBox instance for the notification, and allows access to its properties and methods.

OnClickCheck is signalled (when assigned) from the ClickCheck method. ClickCheck is called from methods like DoChange (private) and KeyDown. This causes OnClickCheck to be signalled when the mouse is clicked on a check box, and when the value for the current item is Toggled using the Space key.

OnClickCheck is signalled before other event handlers like OnItemClick, OnSelectionChange, and OnClick.

OnClickCheck and OnItemClick are not signalled when the checked state for an item is changed in code using Checked, State, CheckAll, or Toggle.

Use OnItemClick for the event signalled with the item index for the affected check box in the control.

OnItemClick is a TCheckListClicked property with the event handler signalled when the check box state has been changed for a specific item in the check list control.

OnItemClick can be used to perform actions needed when the check box State has been toggled. Arguments passed to the event handler identify the check list control (Sender) and the position of the check box (Index) in the Items for the control.

Applications must assign an object procedure that implements the signature for the event handler to respond to the notification.

OnItemClick is signalled from the ItemClick method when the control executes its DoChange (private) or KeyDown methods. This means that the event is signalled when a check box is clicked with the mouse, and when the Space key is pressed on a selected item in the control.

OnItemClick is signalled after the OnClickCheck event handler, and before event handlers like OnSelectionChange and OnClick.

OnClickCheck and OnItemClick are not signalled when the checked state for an item is changed in code using Checked, State, CheckAll, or Toggle.

Use OnClickCheck to perform control-level actions needed when a check box is changed.

TCheckListBox is a TCustomCheckListBox descendant which implements a scrollable list box which displays check boxes for each of its items.

Use the Items property to define the caption for entries that appear in the control. Each of the Items can have a state of checked or unchecked (or "grayed" when AllowGrayed is set). Use the properties and methods such as Toggle, CheckAll, Checked, ItemEnabled, and State to maintain the items in the control.

It provides the scrolling, selection, and drawing styles inherited from the ancestor class. It also includes the ability to render its items as a check box, and to respond to mouse or keyboard events when an item is toggled.

Use the event handlers in the class to perform actions needed when one or more items are clicked or change their state value. Use OnItemClick to process item changes individually.

TCheckListBox sets the visibility for properties defined in the ancestor class.