在Windows下执行一个程序，只要用户进行了影响窗口的动作（如改变窗口大小或移动、单击鼠标等）该动作就会触发一个相应的“事件”

系统每次检测到一个事件时，就会给程序发送一个“消息”，从而使程序可以处理该事件。-In a program running under Windows, as long as the user' s actions affect the window (such as changing the size or move the window, click the mouse, etc.) that action would trigger a corresponding " event"　system every time an event is detected, it will to the program sends a " message" , so that the program can handle the event.