MFC消息处理（一）
1、MFC窗口如何与AfxWndProc建立联系。
当一个新的CWnd派生类创建时，在调用CWnd::CreateEx()过程中，MFC都会安装AfxCbtFilterHook()。这个Hook将拦截HCBT_CREATEWND，将窗体的消息处理函数设置为AfxWndProc()。
// wincore.cpp 651 // CWnd::CreateEx函数通过AfxHookWindowCreate函数安插Hook BOOL CWnd::CreateEx(DWORD dwExStyle, LPCTSTR lpszClassName, LPCTSTR lpszWindowName, DWORD dwStyle, int x, int y, int nWidth, int nHeight, HWND hWndParent, HMENU nIDorHMenu, LPVOID lpParam) { // ... // 如果cs中窗体类名为空，PreCreateWindow (见wincore.cpp 714) 将调用 // AfxEndDeferRegisterClass (见wincore.cpp 4431)注册默认窗口类， // 默认注册的窗口消息处理函数是DefWindowProc if (!PreCreateWindow(cs)) { PostNcDestroy(); return FALSE; } // 安插AfxCbtFilterHook AfxHookWindowCreate(this); HWND hWnd = ::AfxCtxCreateWindowEx(cs.dwExStyle, cs.lpszClass, cs.lpszName, cs.style, cs.x, cs.y, cs.cx, cs.cy, cs.hwndParent, cs.hMenu, cs.hInstance, cs.lpCreateParams); if (!AfxUnhookWindowCreate()) PostNcDestroy(); // cleanup if CreateWindowEx fails too soon // ... } // wincore.cpp 609 void AFXAPI AfxHookWindowCreate(CWnd* pWnd) { _AFX_THREAD_STATE* pThreadState = _afxThreadState.GetData(); if (pThreadState->m_pWndInit == pWnd) return; if (pThreadState->m_hHookOldCbtFilter == NULL) { // 安插_AfxCbtFilterHook，因为_AfxCbtFilterHook()是一个基于计算机训练的hook， // 所以windows在激活、创建、销毁、最大化、最小化、移动窗口或改变窗口大小之前， // 会调用_AfxCbtFilterHook() pThreadState->m_hHookOldCbtFilter = ::SetWindowsHookEx(WH_CBT, _AfxCbtFilterHook, NULL, ::GetCurrentThreadId()); if (pThreadState->m_hHookOldCbtFilter == NULL) AfxThrowMemoryException(); } pThreadState->m_pWndInit = pWnd; }
_AfxCbtFilterHook通过SetWindowLongPtr函数将窗口的处理函数替换成AfxWndProc()，同时，在CWnd::m_pfnSuper中保存原来的窗口消息处理函数指针。
// wincore.cpp 472 LRESULT CALLBACK _AfxCbtFilterHook(int code, WPARAM wParam, LPARAM lParam) { _AFX_THREAD_STATE* pThreadState = _afxThreadState.GetData(); if (code != HCBT_CREATEWND) { // 如果不是HCBT_CREATEWND消息，直接忽略。接收到该消息意味着窗口要创建了 return CallNextHookEx(pThreadState->m_hHookOldCbtFilter, code, wParam, lParam); } LPCREATESTRUCT lpcs = ((LPCBT_CREATEWND)lParam)->lpcs; CWnd* pWndInit = pThreadState->m_pWndInit; BOOL bContextIsDLL = afxContextIsDLL; if (pWndInit != NULL || (!(lpcs->style & WS_CHILD) && !bContextIsDLL)) { // ... HWND hWnd = (HWND)wParam; WNDPROC oldWndProc; if (pWndInit != NULL) { AFX_MANAGE_STATE(pWndInit->m_pModuleState); // connect the HWND to pWndInit... pWndInit->Attach(hWnd); // allow other subclassing to occur first pWndInit->PreSubclassWindow(); // 消息处理函数指针，用于存储原来的消息处理函数 WNDPROC *pOldWndProc = pWndInit->GetSuperWndProcAddr(); // 将窗口的消息处理函数设置成AfxWndProc() WNDPROC afxWndProc = AfxGetAfxWndProc(); oldWndProc = (WNDPROC)SetWindowLongPtr(hWnd, GWLP_WNDPROC, (DWORD_PTR)afxWndProc); if (oldWndProc != afxWndProc) *pOldWndProc = oldWndProc; // 保存原来的指针 pThreadState->m_pWndInit = NULL; } // ... } // ... } // wincore.cpp 1048 WNDPROC* CWnd::GetSuperWndProcAddr() { // Note: it is no longer necessary to override GetSuperWndProcAddr // for each control class with a different WNDCLASS. // This implementation now uses instance data, such that the previous // WNDPROC can be anything. return &m_pfnSuper; } // wincore.cpp 392 WNDPROC AFXAPI AfxGetAfxWndProc() { // 静态库版本的消息处理函数 return &AfxWndProc; }
微软不将AfxWndProc()做为注册窗口过程的原因是DefWindowPorc()可以支持3D控件。这些控件都在微软的CTL3D.dll中。如果系统具有CTL3D功能已经是一种迫切需要，那么应用程序就要覆盖CTL3D的功能（在处理WM_CTLCOLOR消息方面）。为了确保这一点，MFC必须按照以下顺序调用：AfxWndProc()、CTL3D的WndProc()和最后的DefWindowProc()。可见为了确保这一点，微软不得不允许CTL3D在AfxWndProc()之前分类，这就意味着延迟AfxWndProc()的引入。
// wincore.cpp 375 LRESULT CALLBACK AfxWndProc(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam) { // special message which identifies the window as using AfxWndProc if (nMsg == WM_QUERYAFXWNDPROC) return 1; // all other messages route through message map CWnd* pWnd = CWnd::FromHandlePermanent(hWnd); if (pWnd == NULL || pWnd->m_hWnd != hWnd) return ::DefWindowProc(hWnd, nMsg, wParam, lParam); return AfxCallWndProc(pWnd, hWnd, nMsg, wParam, lParam); // 调用AfxCallWndProc } // wincore.cpp 208 LRESULT AFXAPI AfxCallWndProc(CWnd* pWnd, HWND hWnd, UINT nMsg, WPARAM wParam = 0, LPARAM lParam = 0) { _AFX_THREAD_STATE* pThreadState = _afxThreadState.GetData(); MSG oldState = pThreadState->m_lastSentMsg; // 保存最后发送消息 pThreadState->m_lastSentMsg.hwnd = hWnd; pThreadState->m_lastSentMsg.message = nMsg; pThreadState->m_lastSentMsg.wParam = wParam; pThreadState->m_lastSentMsg.lParam = lParam; // Catch exceptions thrown outside the scope of a callback // in debug builds and warn the user. LRESULT lResult; #ifndef _AFX_NO_OCC_SUPPORT // special case for WM_DESTROY if ((nMsg == WM_DESTROY) && (pWnd->m_pCtrlCont != NULL)) pWnd->m_pCtrlCont->OnUIActivate(NULL); #endif // special case for WM_INITDIALOG CRect rectOld; DWORD dwStyle = 0; if (nMsg == WM_INITDIALOG) _AfxPreInitDialog(pWnd, &rectOld, &dwStyle); // 使对话框自动置于窗口中间 // 委托给对象的WindowProc，覆盖该函数，可以在MFC查看某个消息之前处理这个消息 lResult = pWnd->WindowProc(nMsg, wParam, lParam); // more special case for WM_INITDIALOG if (nMsg == WM_INITDIALOG) _AfxPostInitDialog(pWnd, rectOld, dwStyle); pThreadState->m_lastSentMsg = oldState; return lResult; } // wincore.cpp 1737 LRESULT CWnd::WindowProc(UINT message, WPARAM wParam, LPARAM lParam) { // OnWndMsg does most of the work, except for DefWindowProc call LRESULT lResult = 0; if (!OnWndMsg(message, wParam, lParam, &lResult)) // wincore.cpp 1746 lResult = DefWindowProc(message, wParam, lParam); return lResult; }
OnWndMsg函数很大，它首先过滤出WM_COMMAND、WM_NOTIFY、WM_ACTIVE和WM_SETCURSOR。对于这几个消息，框架有自己的处理方法。如果不是这几个，OnWndMsg会在消息映射表中查找消息。MFC维护着一个消息映射表入口缓存，可以通过散列值访问它。