对钩子的理解

Hook
Hooking - Wikipedia：In computer programming, the term hooking covers a range of techniques used to alter or augment the behavior of an operating system, of applications, or of other software components by intercepting function calls or messages or events passed between software components. Code that handles such intercepted function calls, events or messages is called a hook.
最后一句，即：用来处理例如“被拦截的函数调用、事件、消息”的代码都叫钩子
总结：Hook 的意思是钩住，也就是在消息过去之前，先把消息钩住，不让其传递，使用户可以优先处理。给了用户在添加自己的代码的机会，但又不会触及源码。