By default, the Notifier property is 0, which indicates that the property has no effect. Set the Notifier property to a window that you want to receive notification of the control through the WM_COMMAND message. For instance, in VFP or C++ it would be easier to handle the events of the control using the WM_COMMAND messages, rather than using sink interfaces. 

The wParam parameter of the WM_COMMAND message carries the identifier of the event which occurred like listed bellow:

• 0 ( exSelectItem ),  occurs when the user selects/clicks an item
• 1 ( exCheckItem ),  occurs when the user clicks the item's check box, or check the item's checkbox
• 2 ( exUncheckItem ),  occurs when the user clicks the item's check box, or uncheck the item's checkbox
• 3 ( exEditChangeItem ),  occurs when the content of the item's editor is changed.

The lParam parameter of the WM_COMMAND message carries the identifier of the item who fired the event. You can use the Item property to access the control's item giving its identifier. The ID property specifies the item's identifier.

In VFP, you have to assign the hWnd property of the form to the Notifier property of the control as follows:

toolbar.Notifier = thisform.HWnd

while the following code:

BINDEVENT( thisform.HWnd, 273, thisform, "oncommand" )

LPARAMETERS hWnd, uMsg, wParam, lParam

?wParam

*CheckItem
IF ( wParam = 1 ) then
	thisform.toolbar_CheckItem(lParam)
ELSE
	* UncheckItem
	IF ( wParam = 2 ) then
		thisform.toolbar_UncheckItem(lParam)
	ENDIF
ENDIF