WTL 学习笔记 -- 消息流

WTL 学习笔记 -- 消息流

 

正如刚从DOS转到Win32下写程序时，总是为找不到main函数而感到不爽，学习时WTL时，第一反应是找GetMessage和DispatchMessage，想知道消息是如何分发到窗口的。

 

在_tWinMain里做了一些初始化函数之后，就进入了Run函数，显然Run函数就是消息循环。下面是Run函数的代码：

 

int Run(LPTSTR /*lpstrCmdLine*/ = NULL, int nCmdShow = SW_SHOWDEFAULT) {          CMessageLoop theLoop;          _Module.AddMessageLoop(&theLoop);            CMainFrame wndMain;            if(wndMain.CreateEx() == NULL)          {                    ATLTRACE(_T("Main window creation failed!/n"));                    return 0;          }            wndMain.ShowWindow(nCmdShow);            int nRet = theLoop.Run();            _Module.RemoveMessageLoop();          return nRet; }

 

不出所料，CmessageLoop就是用作消息循环的类，_Module.AddMessageLoop不过是保存一个全局引用，其它地方可以方便的取得CmessageLoop的实例theLoop。

 

CmessageLoop::Run函数无疑就是消息循环函数了:

int Run()          {                    BOOL bDoIdle = TRUE;                    int nIdleCount = 0;                    BOOL bRet;                      for(;;)                    {                             while(bDoIdle && !::PeekMessage(&m_msg, NULL, 0, 0, PM_NOREMOVE))                             {                                      if(!OnIdle(nIdleCount++))                                                bDoIdle = FALSE;                             }                               bRet = ::GetMessage(&m_msg, NULL, 0, 0);                               if(bRet == -1)                             {                                      ATLTRACE2(atlTraceUI, 0, _T("::GetMessage returned -1 (error)/n"));                                      continue;   // error, don't process                             }                             else if(!bRet)                             {                                      ATLTRACE2(atlTraceUI, 0, _T("CMessageLoop::Run - exiting/n"));                                      break;   // WM_QUIT, exit message loop                             }                               if(!PreTranslateMessage(&m_msg))                             {                                      ::TranslateMessage(&m_msg);                                      ::DispatchMessage(&m_msg);                             }                               if(IsIdleMessage(&m_msg))                             {                                      bDoIdle = TRUE;                                      nIdleCount = 0;                             }                    }                      return (int)m_msg.wParam;          }

 

CmessageLoop::Run函数，不断的从消息队列里取消息，然后分发给对应的窗口。当消息分发到窗口时，自然就是调用窗口的WINPROC函数了。那么WINPROC是在哪里注册，在哪里实现的呢？

HWND CwindowImpl::Create(HWND hWndParent, RECT& rcPos, LPCTSTR szWindowName = NULL,                             DWORD dwStyle = 0, DWORD dwExStyle = 0,                             UINT nID = 0, LPVOID lpCreateParam = NULL)          {                    if (T::GetWndClassInfo().m_lpszOrigName == NULL)                             T::GetWndClassInfo().m_lpszOrigName = GetWndClassName();                    ATOM atom = T::GetWndClassInfo().Register(&m_pfnSuperWindowProc);                      dwStyle = T::GetWndStyle(dwStyle);                    dwExStyle = T::GetWndExStyle(dwExStyle);                      return CWindowImplBaseT< TBase, TWinTraits >::Create(hWndParent, rcPos, szWindowName,                             dwStyle, dwExStyle, nID, atom, lpCreateParam);          }

 

原来在窗口创建函数里注册WinClass，因为这是在基类里实现的，它需要从子类窗口中获得WinClass信息。很明显，这里调用GetWndClassInfo获得WinClass信息。但是我们并没有看到子类里实现该函数，应该是宏展开的吧，DECLARE_XXXX_WND_CLASS之类最为可疑：

#define DECLARE_FRAME_WND_CLASS(WndClassName, uCommonResourceID) / static CFrameWndClassInfo& GetWndClassInfo() / { /          static CFrameWndClassInfo wc = /          { /                    { 0, StartWindowProc, /                      0, 0, NULL, NULL, NULL, (HBRUSH)(COLOR_WINDOW + 1), NULL, WndClassName }, /                    NULL, NULL, IDC_ARROW, TRUE, 0, _T(""), uCommonResourceID /          }; /          return wc; / }

 

没错，就是它，原来WINPROC函数名为StartWindowProc。问题又来了：StartWindowProc在哪里实现了，子类没有，自然是基类里了：

 

template <class TBase, class TWinTraits> LRESULT CALLBACK CWindowImplBaseT< TBase, TWinTraits >::StartWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {          CWindowImplBaseT< TBase, TWinTraits >* pThis = (CWindowImplBaseT< TBase, TWinTraits >*)_Module.ExtractCreateWndData();          ATLASSERT(pThis != NULL);          pThis->m_hWnd = hWnd;          pThis->m_thunk.Init(pThis->GetWindowProc(), pThis);          WNDPROC pProc = (WNDPROC)&(pThis->m_thunk.thunk);          WNDPROC pOldProc = (WNDPROC)::SetWindowLong(hWnd, GWL_WNDPROC, (LONG)pProc); #ifdef _DEBUG          // check if somebody has subclassed us already since we discard it          if(pOldProc != StartWindowProc)                    ATLTRACE2(atlTraceWindowing, 0, _T("Subclassing through a hook discarded./n")); #else          pOldProc; // avoid unused warning #endif          return pProc(hWnd, uMsg, wParam, lParam); }

 

这个函数的实现有点晦涩，主要是不太明白thunk指的是什么。基本功能倒是很明显，只是重新设置了一下WINPROC，也就是说WINPROC被换成新的了，下次再也不会调用StartWindowProc了。很快找到了真正的WINPROC：

template <class TBase, class TWinTraits> LRESULT CALLBACK CWindowImplBaseT< TBase, TWinTraits >::WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {          CWindowImplBaseT< TBase, TWinTraits >* pThis = (CWindowImplBaseT< TBase, TWinTraits >*)hWnd;          // set a ptr to this message and save the old value          MSG msg = { pThis->m_hWnd, uMsg, wParam, lParam, 0, { 0, 0 } };          const MSG* pOldMsg = pThis->m_pCurrentMsg;          pThis->m_pCurrentMsg = &msg;          // pass to the message map to process          LRESULT lRes;          BOOL bRet = pThis->ProcessWindowMessage(pThis->m_hWnd, uMsg, wParam, lParam, lRes, 0);          // restore saved value for the current message          ATLASSERT(pThis->m_pCurrentMsg == &msg);          pThis->m_pCurrentMsg = pOldMsg;          // do the default processing if message was not handled          if(!bRet)          {                   if(uMsg != WM_NCDESTROY)                             lRes = pThis->DefWindowProc(uMsg, wParam, lParam);                    else                    {                             // unsubclass, if needed                             LONG pfnWndProc = ::GetWindowLong(pThis->m_hWnd, GWL_WNDPROC);                             lRes = pThis->DefWindowProc(uMsg, wParam, lParam);                             if(pThis->m_pfnSuperWindowProc != ::DefWindowProc && ::GetWindowLong(pThis->m_hWnd, GWL_WNDPROC) == pfnWndProc)                                      ::SetWindowLong(pThis->m_hWnd, GWL_WNDPROC, (LONG)pThis->m_pfnSuperWindowProc);                             // clear out window handle                             HWND hWnd = pThis->m_hWnd;                             pThis->m_hWnd = NULL;                             // clean up after window is destroyed                             pThis->OnFinalMessage(hWnd);                    }          }          return lRes; }

 

在这个函数里，调用ProcessWindowMessage去分发消息，ProcessWindowMessage是在哪里实现的呢？没有找到自然是宏展开的：

#define BEGIN_MSG_MAP(theClass) / public: /          BOOL ProcessWindowMessage(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam, LRESULT& lResult, DWORD dwMsgMapID = 0) /          { /                    BOOL bHandled = TRUE; /                    hWnd; /                    uMsg; /                    wParam; /                    lParam; /                    lResult; /                    bHandled; /                    switch(dwMsgMapID) /                    { / #define MESSAGE_HANDLER(msg, func) /          if(uMsg == msg) /          { /                    bHandled = TRUE; /                    lResult = func(uMsg, wParam, lParam, bHandled); /                    if(bHandled) /                             return TRUE; /          } #define END_MSG_MAP() /                             break; /                    default: /                             ATLTRACE2(atlTraceWindowing, 0, _T("Invalid message map ID (%i)/n"), dwMsgMapID); /                             ATLASSERT(FALSE); /                             break; /                    } /                    return FALSE; /          }

原来BEGIN_MSG_MAP等函数就是用展开ProcessWindowMessage函数的，而ProcessWindowMessage又是为用来实现WinProc函数的，这下消息的流动过程就很清楚了。

 

另外与消息处理函数的两个类是CmessageFilter和CidleHandler，两者都是接口类，各定义了一个纯虚函数。在子类里实现它们，然后注册到CMessageLoop中去，CMessageLoop会在适当的时候调用它们。前者一般来转换快捷键，后者一般用来更新界面。