When the user presses the mouse on the discipline, WINDOW is placed in the MFC in the main frame window message queue, and then transforms it first, then transfer the mouse message to the view object, if the view class is not in the view This message is mapped in the class message mapping table (ie the view does not provide a processor), then the MFC retransmit a message to the document object. If this message is not mapped in the document class message mapping table, the MFC retransmits the message to the main window class. If the main window is not, it is sent to the application. If there is no map processing, it is processed by default. Therefore, the mouse message processing function should be added to the view.
