MFC的来龙去脉-----消息处理，找处理函数

一、处理函数的源头

　　对于对话框程序，(无论是模式还是非模式)，在注册窗口的时候，会指定其窗口过程处理函数WinProc；当消息找到了对应的窗口，DispatchMessage便开始让内核user32.dll执行WinProc，它负责调用真正的消息处理函数；

if (pState->m_msgCur.message != WM_KICKIDLE && !AfxPreTranslateMessage(&(pState->m_msgCur)))//将消息分发至各个窗口{  　　::TranslateMessage(&(pState->m_msgCur)); //消息解析　　::DispatchMessage(&(pState->m_msgCur)); //最终由内核调用WinProc,从而调用消息对应的处理函数} return TRUE;

　　有必要搞清楚WinProc是如何指定的。可以详见以下文章：

     http://www.yesky.com/20010202/157454_1.shtml 或 http://www.cnblogs.com/feng801/archive/2010/05/21/1740971.html

二、路径

　　DispatchMessage->user32.dll->AfxWinProc->AfxCallWndProc->【pWnd->WindowProc】->【pWnd->OnWndMsg】

　　为什么要采用【DispatchMessage->user32.dll->AfxWinProc-】如此复杂的windows回调机制?因为Windows想把控在不同进程间窗口间的消息处理的程序状态。通过消回调函数的返回，它可以分配不同时间片给不同任务。据说这部分是windows除COM外最难懂的。

　　注意pWnd，CWnd* pWnd = CWnd::FromHandlePermanent(hWnd)，也即指向Msg指定的目标窗口。该对象的虚函数若有重载，一定是调用已重载，而不是基类的；

　　在【pWnd->OnWndMsg】之后，消息将有三个主要流向，一种是WM_COMMAND的处理，一种是WM_NOTIFY处理，一种直接搜索MessageMap；<深入浅出MFC>中，侯杰详细介绍了这三种流向，及这样的设计带来的好处。其中WM_COMMAND的处理非常有意思，也可参考：

     http://blog.csdn.net/zhangxinrun/article/details/5797154

　　在【pWnd->OnWndMsg】处理后，若能找到消息处理入口，最好；若不能，则只能调用默认的处理函数DefWindowProc；它是windows的缺省消息处理函数。

　　

三、详情

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);   //检查窗口对象是否和windows窗口的句柄一一对应,pWnd后续的虚函数重载后的真正的执行对象    ASSERT(pWnd != NULL);                        ASSERT(pWnd==NULL || pWnd->m_hWnd == hWnd);    if (pWnd == NULL || pWnd->m_hWnd != hWnd)    //若没有句柄对应，说明是一个无窗口的线程，调用默认处理函数        return ::DefWindowProc(hWnd, nMsg, wParam, lParam);    return AfxCallWndProc(pWnd, hWnd, nMsg, wParam, lParam); //否则继续
}

pWnd->WindowProc意味着不同窗口，可以重载该函数，执行各自的WindowProc，前提是，各自窗口都注册了，并指定了相应的Proc函数；

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;   // save for nesting    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;    TRY    {#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);        // delegate to object's WindowProc        lResult = pWnd->WindowProc(nMsg, wParam, lParam);        // more special case for WM_INITDIALOG        if (nMsg == WM_INITDIALOG)            _AfxPostInitDialog(pWnd, rectOld, dwStyle);    }    CATCH_ALL(e)    {        lResult = AfxProcessWndProcException(e, &pThreadState->m_lastSentMsg);        TRACE(traceAppMsg, 0, "Warning: Uncaught exception in WindowProc (returning %ld).\n",            lResult);        DELETE_EXCEPTION(e);    }    END_CATCH_ALL    pThreadState->m_lastSentMsg = oldState;    return lResult;}

Winproc调用OnWndMsg，非常关键的消息路由函数

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))        lResult = DefWindowProc(message, wParam, lParam);    return lResult;}

虚函数的妙用，注意OnWndMsg实际执行的是pWnd所指对象的OnWndMsg;它让消息的游走兵分三路(实际上还有一些special case，但我们主要关心三种去向)：

BOOL CWnd::OnWndMsg(UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult){    LRESULT lResult = 0;    union MessageMapFunctions mmf;    mmf.pfn = 0;    CInternalGlobalLock winMsgLock;    // special case for commands      //第一路，WM_COMMAND命令走这里    if (message == WM_COMMAND)    {        if (OnCommand(wParam, lParam))        {            lResult = 1;            goto LReturnTrue;        }        return FALSE;    }    // special case for notifies           //第二路，WM_NOTIFY消息走这里    if (message == WM_NOTIFY)                          {        NMHDR* pNMHDR = (NMHDR*)lParam;        if (pNMHDR->hwndFrom != NULL && OnNotify(wParam, lParam, &lResult))            goto LReturnTrue;        return FALSE;    }    // special case for activation    if (message == WM_ACTIVATE)        _AfxHandleActivate(this, wParam, CWnd::FromHandle((HWND)lParam));    // special case for set cursor HTERROR    if (message == WM_SETCURSOR &&        _AfxHandleSetCursor(this, (short)LOWORD(lParam), HIWORD(lParam)))    {        lResult = 1;        goto LReturnTrue;    }   // special case for windows that contain windowless ActiveX controls   BOOL bHandled;   bHandled = FALSE;   if ((m_pCtrlCont != NULL) && (m_pCtrlCont->m_nWindowlessControls > 0))   {      if (((message >= WM_MOUSEFIRST) && (message <= AFX_WM_MOUSELAST)) ||         ((message >= WM_KEYFIRST) && (message <= WM_IME_KEYLAST)) ||         ((message >= WM_IME_SETCONTEXT) && (message <= WM_IME_KEYUP)))      {         bHandled = m_pCtrlCont->HandleWindowlessMessage(message, wParam, lParam, &lResult);      }   }   if (bHandled)   {      goto LReturnTrue;   }

　　//第三路，在MessageMap中查找，从子类到基类，逐个寻找消息处理函数入口！此路径将处理绝大多数winodws消息；    const AFX_MSGMAP* pMessageMap; pMessageMap = GetMessageMap();     UINT iHash; iHash = (LOWORD((DWORD_PTR)pMessageMap) ^ message) & (iHashMax-1);    winMsgLock.Lock(CRIT_WINMSGCACHE);    AFX_MSG_CACHE* pMsgCache; pMsgCache = &_afxMsgCache[iHash];    const AFX_MSGMAP_ENTRY* lpEntry;    if (message == pMsgCache->nMsg && pMessageMap == pMsgCache->pMessageMap)    {        // cache hit        lpEntry = pMsgCache->lpEntry;        winMsgLock.Unlock();        if (lpEntry == NULL)            return FALSE;        // cache hit, and it needs to be handled        if (message < 0xC000)            goto LDispatch;        else            goto LDispatchRegistered;    }    else    {        // not in cache, look for it        pMsgCache->nMsg = message;        pMsgCache->pMessageMap = pMessageMap;

        for (/* pMessageMap already init'ed */; pMessageMap->pfnGetBaseMap != NULL;             pMessageMap = (*pMessageMap->pfnGetBaseMap)())        {            // Note: catch not so common but fatal mistake!!            //      BEGIN_MESSAGE_MAP(CMyWnd, CMyWnd)            ASSERT(pMessageMap != (*pMessageMap->pfnGetBaseMap)());            if (message < 0xC000)            {                // constant window message                if ((lpEntry = AfxFindMessageEntry(pMessageMap->lpEntries,                    message, 0, 0)) != NULL)                {                    pMsgCache->lpEntry = lpEntry;                    winMsgLock.Unlock();                    goto LDispatch;                }            }            else            {                // registered windows message                lpEntry = pMessageMap->lpEntries;                while ((lpEntry = AfxFindMessageEntry(lpEntry, 0xC000, 0, 0)) != NULL)                {                    UINT* pnID = (UINT*)(lpEntry->nSig);                    ASSERT(*pnID >= 0xC000 || *pnID == 0);                        // must be successfully registered                    if (*pnID == message)                    {                        pMsgCache->lpEntry = lpEntry;                        winMsgLock.Unlock();                        goto LDispatchRegistered;                    }                    lpEntry++;      // keep looking past this one                }            }        }        pMsgCache->lpEntry = NULL;        winMsgLock.Unlock();        return FALSE;    }LDispatch:    ASSERT(message < 0xC000);    mmf.pfn = lpEntry->pfn;    switch (lpEntry->nSig)    {    default:        ASSERT(FALSE);        break;    case AfxSig_l_p:        {            CPoint point(lParam);                    lResult = (this->*mmf.pfn_l_p)(point);            break;        }            case AfxSig_b_D_v:        lResult = (this->*mmf.pfn_b_D)(CDC::FromHandle(reinterpret_cast<HDC>(wParam)));        break;
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