【转】Windows消息投递流程：一般窗口消息投递（WM_LBUTTONCLICK）

原文网址：http://blog.csdn.net/hyhnoproblem/article/details/6182646

本例通过在单文档程序的视图中添加WM_LBUTTONCLICK消息处理函数，来解释一般窗口消息的投递流程。 基于VS 2005

BEGIN_MESSAGE_MAP(CMyView, CView)
    ON_WM_LBUTTONDBLCLK()
END_MESSAGE_MAP()
// ON_WM_LBUTTONDBLCLK宏展开
#define ON_WM_LBUTTONDBLCLK() /
{ WM_LBUTTONDBLCLK, 0, 0, 0, AfxSig_vwp, /
    (AFX_PMSG)(AFX_PMSGW) /
    (static_cast< void (AFX_MSG_CALL CWnd::*)(UINT, CPoint) > ( &ThisClass :: OnLButtonDblClk)) },

从上面的代码可以看出WM_LBUTTONCLICK消息的类型标签是AfxSig_vwp， 在afxmsg_.h中有一个枚举类型AfxSig，消息标签主要用于区分消息处理函数的类型。该类型中定义了AfxSig_vwp的值：

enum AfxSig
{
    //...
    AfxSig_vWp = AfxSig_v_W_p
    //...
}

在AfxWndProc中，将消息中的句柄映射成窗口类指针，这个指针指向CMyView。AfxWndProc调用AfxCallWndProc，AfxCallWndProc调用CWnd::WindowProc，CWnd::WindowProc调用CWnd::OnWndMsg，CWnd::OnWndMsg完成对消息的处理。

// wincore.cpp 1746
BOOL CWnd::OnWndMsg(UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult)
{
    // ...
    // GetMessageMap是个虚函数，因为当前指针是指向CMyView，所以取到的是CMyView的消息映射表
    const AFX_MSGMAP* pMessageMap; pMessageMap = GetMessageMap();
    UINT iHash; iHash = (LOWORD((DWORD_PTR)pMessageMap) ^ message) & (iHashMax-1);
    winMsgLock.Lock(CRIT_WINMSGCACHE);
    // 全局消息散列缓存，查找缓存
    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;     // 系统消息？
        else
            goto LDispatchRegistered;       // 已注册消息？
    }
    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:
    mmf.pfn = lpEntry->pfn;
    switch (lpEntry->nSig)
    {
        //...
    case AfxSig_v_u_p:      // 消息标签
        {
            CPoint point(lParam);
            (this->*mmf.pfn_v_u_p)(static_cast<UINT>(wParam), point);
        }
        break;
        //...
    }
    //...
LDispatchRegistered:    // for registered windows messages
    ASSERT(message >= 0xC000);
    ASSERT(sizeof(mmf) == sizeof(mmf.pfn));
    mmf.pfn = lpEntry->pfn;
    lResult = (this->*mmf.pfn_l_w_l)(wParam, lParam);
}
// 消息处理函数类型枚举
union MessageMapFunctions
{
    AFX_PMSG pfn;   // generic member function pointer
    // ...
    LRESULT (AFX_MSG_CALL CWnd::*pfn_l_w_l)(WPARAM, LPARAM);
};