方法8 : GetMsgProc Function
The GetMsgProc function is an application-defined or library-defined callback function used with the SetWindowsHookEx function. The system calls this function whenever the GetMessage or PeekMessage function has retrieved a message from an application message queue. Before returning the retrieved message to the caller, the system passes the message to the hook procedure.
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GetMsgProc是和SetWindowsHookEx方法一起使用的、程序定义的或者库定义的回调函数。无论什么时候，当GetMessage 或者 PeekMessage方法接收到来自应用程序消息队列的消息时，系统都会调用该方法。在将收到的消息返回给调用者之前，系统将消息传递给钩子子程。
The HOOKPROC type defines a pointer to this callback function. GetMsgProc is a placeholder for the application-defined or library-defined function name. HOOKPROC类型定义了指向该回调函数的指针。GetMsgProc是程序定义的或者库定义的方法名字。
Syntax 语法
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LRESULT CALLBACK GetMsgProc(
int code,
WPARAM wParam,
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LPARAM lParam
);
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Parameters 参数
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code ： [in] Specifies whether the hook procedure must process the message. If code is HC_ACTION, the hook procedure must process the message. If code is less than zero, the hook procedure must pass the message to the CallNextHookEx function without further processing and should return the value returned by CallNextHookEx.
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指定钩子子程是否必须处理消息。如果nCode是HC_ACTION，钩子子程就必须处理该消息。如果nCode小于0，钩子子程就必须将该消息传递给CallNextHookEx方法，自己对消息不做进一步处理，并且应该返回由CallNextHookEx方法返回的返回值。
wParam ：[in] Specifies whether the message has been removed from the queue. This parameter can be one of the following values. 指定消息是否已经被从队列中移除了。该参数可以是下列值中的一个：
1．PM_NOREMOVE ：Specifies that the message has not been removed from the queue. (An application called the function, specifying the PM_NOREMOVE flag.)
指定消息尚未从队列中移出。(应用程序在调用该方法的同时指定PM_NOREMOVE标志)
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2．PM_REMOVE Specifies that the message has been removed from the queue. (An application called GetMessage, or it called the PeekMessage function, specifying the PM_REMOVE flag.) 指定消息已经被从队列中移除了。(程序调用GetMessage 或者PeekMessage方法的同时指定PM_REMOVE标志)
lParam ：[in] Pointer to an MSG structure that contains details about the message. 指向MSG结构的指针，结构中包含和消息相关的细节。
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Return Value 返回值
If code is less than zero, the hook procedure must return the value returned by CallNextHookEx. If code is greater than or equal to zero, it is highly recommended that you call CallNextHookEx and return the value it returns; otherwise, other applications that have installed WH_GETMESSAGE hooks will not receive hook notifications and may behave incorrectly as a result. If the hook procedure does not call CallNextHookEx, the return value should be zero.
如果参数code小于0，钩子子程必须返回由CallNextHookEx返回的返回值。
如果参数code大于等于0，强烈要求调用CallNextHookEx方法，并返回由该方法返回的返回值；否则，其他已经安装了WH_GETMESSAGE钩子的程序将收不到钩子通知，可能导致行为的错误。如果钩子子程没有调用CallNextHookEx方法,返回值应该是0
Remarks 备注
The GetMsgProc hook procedure can examine or modify the message. After the hook procedure returns control to the system, the GetMessage or PeekMessage function returns the message, along with any modifications, to the application that originally called it.
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GetMsgProc钩子子程能够检查或者修改消息。在钩子子程将控制权交还给系统之后，GetMessage 或者PeekMessage方法将该消息以及任何修改都一起返回给最初调用它的应用程序。
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An application installs this hook procedure by specifying the WH_GETMESSAGE hook type and a pointer to the hook procedure in a call to the SetWindowsHookEx function.
应用程序通过下面方式安装该钩子子程：指定WH_ GETMESSAGE钩子类型；指定在调用SetWindowsHookEx方法的函数中指向钩子子程的指针。
Helios 2007-4-12