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。