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A parent's OnParentNotify member function is called by the framework when its child window is created or destroyed, or when the user clicks a mouse button while the cursor is over the child window.
Specifies the event for which the parent is being notified and the identifier of the child window. The event is the low-order word of message. If the event is WM_CREATE or WM_DESTROY, the high-order word of message is the identifier of the child window; otherwise, the high-order word is undefined. The event (low-order word of message) can be any of these values:
WM_CREATE The child window is being created.
WM_DESTROY The child window is being destroyed.
WM_LBUTTONDOWN The user has placed the mouse cursor over the child window and clicked the left mouse button.
WM_MBUTTONDOWN The user has placed the mouse cursor over the child window and clicked the middle mouse button.
WM_RBUTTONDOWN The user has placed the mouse cursor over the child window and clicked the right mouse button.
If the event (low-order word) of message is WM_CREATE or WM_DESTROY, lParam specifies the window handle of the child window; otherwise lParam contains the x and y coordinates of the cursor. The x coordinate is in the low-order word and the y coordinate is in the high-order word.
When the child window is being created, the system calls OnParentNotify just before the Create member function that creates the window returns. When the child window is being destroyed, the system calls OnParentNotify before any processing takes place to destroy the window.
OnParentNotify is called for all ancestor windows of the child window, including the top-level window.
All child windows except those that have the WS_EX_NOPARENTNOTIFY style send this message to their parent windows. By default, child windows in a dialog box have the WS_EX_NOPARENTNOTIFY style unless the child window was created without this style by calling the CreateEx member function.
This member function is called by the framework to allow your application to handle a Windows message. The parameters passed to your function reflect the parameters received by the framework when the message was received. If you call the base-class implementation of this function, that implementation will use the parameters originally passed with the message and not the parameters you supply to the function.