模仿Spy++抓某窗口消息

核心函数

SetWindowsHookExA

API文档：https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setwindowshookexa

https://docs.microsoft.com/zh-cn/previous-versions/windows/desktop/legacy/ms644981(v=vs.85)

核心代码：

1、写一个dll。

HWND g_MainWnd = NULL;
HHOOK g_hook = NULL;

#ifdef __cplusplus
extern "C" { //only need to export C interface if
    // used by C++ source code
#endif
    __declspec(dllexport) void SetHHook(HHOOK hook)  //此函数废弃
    {
        g_hook = hook;
    }

    __declspec(dllexport) LRESULT GetMsgProc(int nCode, WPARAM wParam, LPARAM lParam)
    {
        if (nCode == HC_ACTION && wParam == PM_REMOVE)
        {
            //must process and lParam is MSG struct
            MSG* msg = (MSG*)lParam;
            if (g_MainWnd)
            {
                PostMessage(g_MainWnd, WM_USER +  + msg->message, msg->wParam, msg->lParam);
            }
        }

        //晕，第一个参数被忽略的，可以直接传NULL
        return CallNextHookEx(g_hook, nCode, wParam, lParam);
    }

#ifdef __cplusplus
}
#endif

BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
        //try to get the windows
        g_MainWnd = FindWindow(NULL, L"EasySpy");
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}

2、  调用函数

//查看捕获的窗口句柄
        HWND hCaptured = ::WindowFromPoint(point);
        DWORD dwThreadId;
        HOOKPROC hkprcSysMsg=NULL;
        dwThreadId = GetWindowThreadProcessId(hCaptured, NULL);
        if (g_lastHook)
        {
            UnhookWindowsHookEx(g_lastHook);
        }
        //尝试去loaddll
        if (!g_module)
        {
            g_module = LoadLibrary(TEXT("E:\\代码\\开源代码\\hookdemo\\trunk\\EasySpy\\Debug\\DllInject.dll"));
        }
        if (g_module)
        {
            hkprcSysMsg = (HOOKPROC)GetProcAddress(g_module, "GetMsgProc");
        }
        if (hkprcSysMsg)
        {
            //这里去拦截消息
            g_lastHook = SetWindowsHookEx(WH_GETMESSAGE, hkprcSysMsg, g_module, dwThreadId);
        }

完整代码Demo见github：https://github.com/xuhuajie-NetEase/EasySpy

有兴趣的同学可以优化下代码，做成跟spy++更像的。我只是研究下Hook技术，就不再优化了了。