The framework calls this member function when a pop-up menu is about to become active.
This allows an application to modify the pop-up menu before it is displayed without changing the entire menu.
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.