MFC下WM_NOTIFY消息处理流程

参考文章：MFC的消息反射机制

    在前一篇文章：MFC消息处理流程概述中描述了MFC消息处理的大体流程。由CWnd::OnWndMsg函数可知，当消息为WM_NOTIFY消息时，调用的是virtual CWnd::OnNotify处理。

if (message == WM_NOTIFY){    NMHDR* pNMHDR = (NMHDR*)lParam;    if (pNMHDR->hwndFrom != NULL && OnNotify(wParam, lParam, &lResult))goto LReturnTrue;    return FALSE;}

BOOL CWnd::OnNotify(WPARAM, LPARAM lParam, LRESULT* pResult){NMHDR* pNMHDR = (NMHDR*)lParam;HWND hWndCtrl = pNMHDR->hwndFrom;// get the child ID from the window itselfUINT_PTR nID = _AfxGetDlgCtrlID(hWndCtrl);int nCode = pNMHDR->code;// reflect notification to child window controlif (ReflectLastMsg(hWndCtrl, pResult))return TRUE;        // eaten by childAFX_NOTIFY notify;notify.pResult = pResult;notify.pNMHDR = pNMHDR;return OnCmdMsg((UINT)nID, MAKELONG(nCode, WM_NOTIFY), ¬ify, NULL);}

    以上hWndCtrl为子窗口的句柄，通过调用ReflectLastMsg(hWndCtrl, pResult)给子窗口一个自身处理的机会，将消息反射给子窗口处理。ReflectLastMsg返回TRUE，表明子窗口处理了此消息，则OnNotify返回并不交由父窗口处理；反之，表示子窗口未处理此消息，此时，调用OnCmdMsg(...)由父窗口进行处理。    ReflectLastMsg通过层层调用最终会调用CWnd::ReflectChildNotify函数来处理WM_NOTIFY反射消息。

BOOL PASCAL CWnd::ReflectLastMsg(HWND hWndChild, LRESULT* pResult){    CWnd* pWnd = (CWnd*)pMap->LookupPermanent(hWndChild);    return pWnd->SendChildNotifyLastMsg(pResult);}BOOL CWnd::SendChildNotifyLastMsg(LRESULT* pResult){    return OnChildNotify(pThreadState->m_lastSentMsg.message,        pThreadState->m_lastSentMsg.wParam, pThreadState->m_lastSentMsg.lParam, pResult);}BOOL CWnd::OnChildNotify(UINT uMsg, WPARAM wParam, LPARAM lParam, LRESULT* pResult){    return ReflectChildNotify(uMsg, wParam, lParam, pResult);}

    CWnd::ReflectChildNotify函数如下：

BOOL CWnd::ReflectChildNotify(UINT uMsg, WPARAM wParam, LPARAM lParam, LRESULT* pResult){// Note: reflected messages are send directly to CWnd::OnWndMsg//  and CWnd::OnCmdMsg for speed and because these messages are not//  routed by normal OnCmdMsg routing (they are only dispatched)switch (uMsg){        ......case WM_NOTIFY:{// reflect the message through the message map as OCM_NOTIFYNMHDR* pNMHDR = (NMHDR*)lParam;int nCode = pNMHDR->code;AFX_NOTIFY notify;notify.pResult = pResult;notify.pNMHDR = pNMHDR;return CWnd::OnCmdMsg(0, MAKELONG(nCode, WM_REFLECT_BASE+WM_NOTIFY), ¬ify, NULL);}        ......}

    很显然，调用了virtual CWnd::OnCmdMsg函数来处理，实际上是virtual CCmdTarget::OnCmdMsg函数，CWnd继承自CCmdTarget。

注意：以上return CWnd::OnCmdMsg(0, MAKELONG(nCode, WM_REFLECT_BASE+WM_NOTIFY), ¬ify, NULL)语句，在WM_NOTIFY的基础上+WM_REFLECT_BASE，因为消息流程走到这步，是在子控件窗口的消息映射表中查找反射消息处理函数。
    注意区分WM_NOTIFY消息与WM_NOTIFY反射消息，WM_NOTIFY反射消息即消息WM_REFLECT_BASE+WM_NOTIFY，父窗口收到WM_NOTIFY消息而扔给子窗口处理时，为了区分，子窗口处理的消息被译成WM_REFLECT_BASE+WM_NOTIFY消息，否则岂不和子窗口本身的WM_NOTIFY消息混淆了。

BOOL CCmdTarget::OnCmdMsg(UINT nID, int nCode, void* pExtra,AFX_CMDHANDLERINFO* pHandlerInfo){    //从消息映射中查找对应的处理函数    for (pMessageMap = GetMessageMap(); pMessageMap->pfnGetBaseMap != NULL;  pMessageMap = (*pMessageMap->pfnGetBaseMap)()){lpEntry = AfxFindMessageEntry(pMessageMap->lpEntries, nMsg, nCode, nID);if (lpEntry != NULL){// 找到对应的消息处理函数return _AfxDispatchCmdMsg(this, nID, nCode,lpEntry->pfn, pExtra, lpEntry->nSig, pHandlerInfo);}}return FALSE;   // not handled  没有对应的消息处理函数则返回FALSE}

    在子控件窗口类的消息映射表中没有找到对应的WM_REFLECT_BASE+WM_WM_NOTIFY消息（即对应WM_NOTIFY的反射消息）处理函数返回FALSE，也即以上ReflectLastMsg(hWndCtrl, pResult)返回FALSE，这样父窗口就会处理。    否则，在_AfxDispatchCmdMsg函数中会调用对应的反射消息处理函数处理，ReflectLastMsg(hWndCtrl, pResult)返回TRUE，这样父窗口就不会处理了。