钩子函数
钩子函数可以截获并处理其他应用程序的消息。每当特定的消息发出，在没有到达目的窗口前，钩子程序就先捕获该消息，亦即钩子函数先得到控制权。这时钩子函数即可以加工处理（改变）该消息，也可以不作处理而继续传递该消息，还可以强制结束消息的传递。
钩子的种类很多，每种钩子可以截获并处理相应的消息，如键盘钩子可以截获键盘消息，外壳钩子可以截取、启动和关闭应用程序的消息等
关于HOOK
Hooks
A hook is a point in the system message-handling mechanism where an application can install a subroutine to monitor the message traffic in the system and process certain types of messages before they reach the target window procedure.
安装一个HOOK，SetWindowsHookEx
对每种类型的钩子由系统来维护一个钩子链，最近安装的钩子放在链的开始，而最先安装的钩子放在最后，也就是后加入的先获得控制权。
The SetWindowsHookEx function installs an application-defined hook procedure into a hook chain. You would install a hook procedure to monitor the system for certain types of events. These events are associated either with a specific thread or with all threads in the same desktop as the calling thread.
HHOOK SetWindowsHookEx(
int idHook, // hook type.请查看MSDN获得详细信息
HOOKPROC lpfn, // hook procedure
HINSTANCE hMod, // handle to application instance
DWORD dwThreadId // thread identifier
);
得到控制权的钩子函数在完成对消息的处理后，如果想要该消息继续传递，那么它必须调用另外一个SDK中的API函数CallNextHookEx来传递它。
(对一个事件处理的hook可能有多个，它们成链状，使用CallNextHookEx一级一级地调用。简单解释过来就是“调用下一个HOOK” )
CallNextHookEx
The CallNextHookEx function passes the hook information to the next hook procedure in the current hook chain. A hook procedure can call this function either before or after processing the hook information.
LRESULT CallNextHookEx(
HHOOK hhk, // handle to current hook
int nCode, // hook code passed to hook procedure
WPARAM wParam, // value passed to hook procedure
LPARAM lParam // value passed to hook procedure
);
hook处理函数
LRESULT CALLBACK HookProc(
int nCode,
WPARAM wParam,
LPARAM lParam
);
取消HOOK
UnhookWindowsHookEx
The UnhookWindowsHookEx function removes a hook procedure installed in a hook chain by the SetWindowsHookEx function.
BOOL UnhookWindowsHookEx(
HHOOK hhk // handle to hook procedure
);
示例：
[code]
// 监视鼠标消息
// hook处理函数声明
LRESULT CALLBACK MyMouseProc(int nCode, WPARAM wParam, LPARAM lParam);
static BOOL StartWatchingMouse(); // 开始监视
static void StopWatchingMouse(); // 结束
static HHOOK hHook = NULL; //hook指针
/*======================================================
*Function:StartWatchingMouse()
*Author:wuhuiran 05-7-23
*Desc:开始监视鼠标
*Record:
--------------------------------------------------------
========================================================*/
BOOL StartWatchingMouse()
{
hHook = SetWindowHookEx(WM_MOUSE, (HOOKPROC) MyMouseProc,
(HINSTANCE) NULL, GetCurrentThreadId());
if(!hHook)
{
return FALSE;
}
return TRUE;
}
/*======================================================
*Function:StartWatchingMouse()
*Author:wuhuiran 05-7-23
*Desc:取消监视鼠标
*Record:
--------------------------------------------------------
========================================================*/
void StopWatchingMouse()
{
if(hHook)
{
UnHookWindowHookEx(hHook);
hHook = NULL;
}
}
/*======================================================
*Function:StartWatchingMouse()
*Author:wuhuiran 05-7-23
*Desc:HOOK处理函数
*Record:
--------------------------------------------------------
========================================================*/
LRESULT CALLBACK MyMouseProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if(nCode < 0)
{
return CallNextHookEx(hHook, nCode, wParam, lParam);
}
MOUSEHOOKSTRUCT *pMouseHookStruct; //鼠标HOOK结构体
pMouseHookStruct = (MOUSEHOOKSTRUCT *)lParam;
POINT pt = pMouseHookStruct->pt;
//动一下鼠标就会显示鼠标位置
CString strMsg;
strMsg.Format("x:\t%d\ny:\t%d", pt.x, pt.y);
AfxMessageBox(strMsg);
return CallNextHookEx(myHook, nCode, wParam, lParam);
}
[/code]
注意：
hook会使系统变慢，除非必要，不要频繁使用。在不使用的时候尽快删除
全局钩子必须放在DLL中
只是简单介绍了一下钩子函数的使用方法，具体的函数介绍请参阅MSDN和其他文章。