MFC下WM_NOTIFY消息處理流程

參考文章：MFC的消息反射機制

    在前一篇文章：MFC消息處理流程概述中描述了MFC消息處理的大體流程。由CWnd::OnWndMsg函數可知，當消息為WM_NOTIFY消息時，調用的是virtual CWnd::OnNotify處理。

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 itself
    UINT_PTR nID = _AfxGetDlgCtrlID(hWndCtrl);
    int nCode = pNMHDR->code;

    // reflect notification to child window control
    if (ReflectLastMsg(hWndCtrl, pResult))
        return TRUE;        // eaten by child

    AFX_NOTIFY notify;
    notify.pResult = pResult;
    notify.pNMHDR = pNMHDR;
    return OnCmdMsg((UINT)nID, MAKELONG(nCode, WM_NOTIFY), ¬ify, NULL);
}

    以上hWndCtrl為子窗口的句柄，通過調用ReflectLastMsg(hWndCtrl, pResult)給子窗口一個自身處理的機會，將消息反射給子窗口處理。ReflectLastMsg返回TRUE，表明子窗口處理了此消息，則OnNotify返回並不交由父窗口處理；反之，表示子窗口未處理此消息，此時，調用OnCmdMsg(...)由父窗口進行處理。
    ReflectLastMsg通過層層調用最終會調用CWnd::ReflectChildNotify函數來處理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函數如下：

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_NOTIFY
            NMHDR* 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);
        }
        ......
}

    很顯然，調用了virtual CWnd::OnCmdMsg函數來處理，實際上是virtual CCmdTarget::OnCmdMsg函數，CWnd繼承自CCmdTarget。

注意：以上return CWnd::OnCmdMsg(0, MAKELONG(nCode, WM_REFLECT_BASE+WM_NOTIFY), ¬ify, NULL)語句，在WM_NOTIFY的基礎上+WM_REFLECT_BASE，因為消息流程走到這步，是在子控件窗口的消息映射表中查找反射消息處理函數。
    注意區分WM_NOTIFY消息與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消息而扔給子窗口處理時，為了區分，子窗口處理的消息被譯成WM_REFLECT_BASE+WM_NOTIFY消息，否則豈不和子窗口本身的WM_NOTIFY消息混淆了。

BOOL CCmdTarget::OnCmdMsg(UINT nID, int nCode, void* pExtra,
    AFX_CMDHANDLERINFO* pHandlerInfo)
{
    //從消息映射中查找對應的處理函數
    for (pMessageMap = GetMessageMap(); pMessageMap->pfnGetBaseMap != NULL;
      pMessageMap = (*pMessageMap->pfnGetBaseMap)())
    {
        lpEntry = AfxFindMessageEntry(pMessageMap->lpEntries, nMsg, nCode, nID);
        if (lpEntry != NULL)
        {
            // 找到對應的消息處理函數
            return _AfxDispatchCmdMsg(this, nID, nCode,
                lpEntry->pfn, pExtra, lpEntry->nSig, pHandlerInfo);
        }
    }
    return FALSE;   // not handled  沒有對應的消息處理函數則返回FALSE
}

    在子控件窗口類的消息映射表中沒有找到對應的WM_REFLECT_BASE+WM_WM_NOTIFY消息（即對應WM_NOTIFY的反射消息）處理函數返回FALSE，也即以上ReflectLastMsg(hWndCtrl, pResult)返回FALSE，這樣父窗口就會處理。
    否則，在_AfxDispatchCmdMsg函數中會調用對應的反射消息處理函數處理，ReflectLastMsg(hWndCtrl, pResult)返回TRUE，這樣父窗口就不會處理了。

http://blog.csdn.net/hisinwang/article/details/8045382