1、MFC視窗如何與AfxWndProc建立聯絡。

當一個新的CWnd派生類建立時，在呼叫CWnd::CreateEx()過程中，MFC都會安裝AfxCbtFilterHook()。這個Hook將攔截HCBT_CREATEWND，將窗體的訊息處理函式設定為AfxWndProc()。

// wincore.cpp 651 // CWnd::CreateEx函式通過AfxHookWindowCreate函式安插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中窗體類名為空，PreCreateWindow (見wincore.cpp 714) 將呼叫 // AfxEndDeferRegisterClass (見wincore.cpp 4431)註冊預設視窗類， // 預設註冊的視窗訊息處理函式是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，因為_AfxCbtFilterHook()是一個基於計算機訓練的hook， // 所以windows在啟用、建立、銷燬、最大化、最小化、移動視窗或改變視窗大小之前， // 會呼叫_AfxCbtFilterHook() pThreadState->m_hHookOldCbtFilter = ::SetWindowsHookEx(WH_CBT, _AfxCbtFilterHook, NULL, ::GetCurrentThreadId()); if (pThreadState->m_hHookOldCbtFilter == NULL) AfxThrowMemoryException(); } pThreadState->m_pWndInit = pWnd; }

_AfxCbtFilterHook通過SetWindowLongPtr函式將視窗的處理函式替換成AfxWndProc()，同時，在CWnd::m_pfnSuper中儲存原來的視窗訊息處理函式指標。

// 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訊息，直接忽略。接收到該訊息意味著視窗要建立了 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(); // 訊息處理函式指標，用於儲存原來的訊息處理函式 WNDPROC *pOldWndProc = pWndInit->GetSuperWndProcAddr(); // 將視窗的訊息處理函式設定成AfxWndProc() WNDPROC afxWndProc = AfxGetAfxWndProc(); oldWndProc = (WNDPROC)SetWindowLongPtr(hWnd, GWLP_WNDPROC, (DWORD_PTR)afxWndProc); if (oldWndProc != afxWndProc) *pOldWndProc = oldWndProc; // 儲存原來的指標 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() { // 靜態庫版本的訊息處理函式 return &AfxWndProc; }

微軟不將AfxWndProc()做為註冊視窗過程的原因是DefWindowPorc()可以支援3D控制元件。這些控制元件都在微軟的CTL3D.dll中。如果系統具有CTL3D功能已經是一種迫切需要，那麼應用程式就要覆蓋CTL3D的功能（在處理WM_CTLCOLOR訊息方面）。為了確保這一點，MFC必須按照以下順序呼叫：AfxWndProc()、CTL3D的WndProc()和最後的DefWindowProc()。可見為了確保這一點，微軟不得不允許CTL3D在AfxWndProc()之前分類，這就意味著延遲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); // 呼叫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; // 儲存最後傳送訊息 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); // 使對話方塊自動置於視窗中間 // 委託給物件的WindowProc，覆蓋該函式，可以在MFC檢視某個訊息之前處理這個訊息 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函式很大，它首先過濾出WM_COMMAND、WM_NOTIFY、WM_ACTIVE和WM_SETCURSOR。對於這幾個訊息，框架有自己的處理方法。如果不是這幾個，OnWndMsg會在訊息對映表中查詢訊息。MFC維護著一個訊息對映表入口快取，可以通過雜湊值訪問它。