关闭对话框时的消息响应

1)点击OK按钮:OnOk-WM_DESTROY  
        2)   点击Cancel按钮:OnCancel-WM_DESTROY  
        3)   点击×按钮:WM_CLOSE-ONCANCEL-WM_DESTROY  
        4)   键盘ESC按键:OnCancel-WM_DESTROY  
        5)调用EndDialog(IDCANCEL),直接到WM_DESTROY消息  
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