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该示例通过研究基本的单文档程序的“文件”－－“打开”命令，分析WM_COMMAND消息投递流程。基于VS 2005 代码

AfxWndProc最终调用的是OnWndMsg，这个函数负责消息的分发处理。当消息是WM_COMMAND时，将消息投递给OnCommand函数。

// wincore.cpp 1746<br /> BOOL CWnd::OnWndMsg(UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult)<br /> {<br /> LRESULT lResult = 0;<br /> union MessageMapFunctions mmf;<br /> mmf.pfn = 0;<br /> CInternalGlobalLock winMsgLock;<br /> // special case for commands<br /> if (message == WM_COMMAND)<br /> {<br /> if (OnCommand(wParam, lParam))<br /> {<br /> lResult = 1;<br /> goto LReturnTrue;<br /> }<br /> return FALSE;<br /> }<br /> //...<br /> }<br />  

OnCommand是个虚函数，因为消息是主窗口产生的，所以调用的是CFrameWnd::OnCommand函数该函数先检查该消息是不是在线请求帮助，如果是，则程序给框架窗口发送一个WM_COMMANDHELP消息，否则交由基类CWnd::OnCommand()处理。

// winfrm.cpp 299<br /> BOOL CFrameWnd::OnCommand(WPARAM wParam, LPARAM lParam)<br /> // return TRUE if command invocation was attempted<br /> {<br /> HWND hWndCtrl = (HWND)lParam;<br /> UINT nID = LOWORD(wParam);<br /> CFrameWnd* pFrameWnd = GetTopLevelFrame();<br /> ENSURE_VALID(pFrameWnd);<br /> if (pFrameWnd->m_bHelpMode && hWndCtrl == NULL &&<br /> nID != ID_HELP && nID != ID_DEFAULT_HELP && nID != ID_CONTEXT_HELP)<br /> {<br /> // route as help<br /> if (!SendMessage(WM_COMMANDHELP, 0, HID_BASE_COMMAND+nID))<br /> SendMessage(WM_COMMAND, ID_DEFAULT_HELP);<br /> return TRUE;<br /> }<br /> // route as normal command<br /> return CWnd::OnCommand(wParam, lParam);<br /> }<br />  

CWnd::OnCommand首先检查表示控件的LPARAM。如果消息是由控件产生的，LPARAM就会包含控件窗口句柄。如果消息是控件通知，框架就会执行特定的处理过程。如果消息是为某个控件产生的，OnCommand会将消息直接发送给控件，然后OnCommand返回。否则，CWnd::OnCommand()要确保产生命令的界面元素没有被禁用，然后将消息传递给OnCmdMsg函数，调用的是CFrameWnd::OnCmdMsg函数

// wParam<br /> // The high-order word specifies the notification code if the message is from a control.<br /> // If the message is from an accelerator, this value is 1. If the message is from a menu,<br /> // this value is zero.<br /> // The low-order word specifies the identifier of the menu item, control, or accelerator.<br /> // lParam<br /> // Handle to the control sending the message if the message is from a control.<br /> // Otherwise, this parameter is NULL.<br /> BOOL CWnd::OnCommand(WPARAM wParam, LPARAM lParam)<br /> // return TRUE if command invocation was attempted<br /> {<br /> UINT nID = LOWORD(wParam);<br /> HWND hWndCtrl = (HWND)lParam;<br /> int nCode = HIWORD(wParam);<br /> // default routing for command messages (through closure table)<br /> if (hWndCtrl == NULL)<br /> { // 菜单命令先走这里<br /> // zero IDs for normal commands are not allowed<br /> if (nID == 0)<br /> return FALSE;<br /> // make sure command has not become disabled before routing<br /> CTestCmdUI state;<br /> state.m_nID = nID;<br /> OnCmdMsg(nID, CN_UPDATE_COMMAND_UI, &state, NULL); // CFrameWnd::OnCmdMsg<br /> if (!state.m_bEnabled)<br /> {<br /> TRACE(traceAppMsg, 0, "Warning: not executing disabled command %d/n", nID);<br /> return TRUE;<br /> }<br /> // menu or accelerator<br /> nCode = CN_COMMAND;<br /> }<br /> else<br /> {<br /> // ToolBar命令走这里，或控件通知<br /> // control notification<br /> ASSERT(nID == 0 || ::IsWindow(hWndCtrl));<br /> if (_afxThreadState->m_hLockoutNotifyWindow == m_hWnd)<br /> return TRUE; // locked out - ignore control notification<br /> // reflect notification to child window control<br /> if (ReflectLastMsg(hWndCtrl))<br /> return TRUE; // eaten by child<br /> // zero IDs for normal commands are not allowed<br /> if (nID == 0)<br /> return FALSE;<br /> }<br /> // 调用CFrameWnd::OnCmdMsg<br /> return OnCmdMsg(nID, nCode, NULL, NULL);<br /> }<br />  

CFrameWnd::OnCmdMsg函数调用时，pExtra和pHandlerInfo是NULL，因为处理命令不需要这一信息。取出的消息按照以下顺序经过应用程序的各个部分：活动视图、活动视图的文档、文档模板、主窗口、应用程序。

// winfrm.cpp 880<br /> BOOL CFrameWnd::OnCmdMsg(UINT nID, int nCode, void* pExtra,<br /> AFX_CMDHANDLERINFO* pHandlerInfo)<br /> {<br /> CPushRoutingFrame push(this);<br /> // 将消息传递给活动视图，调用CView::OnCmdMsg<br /> CView* pView = GetActiveView();<br /> if (pView != NULL && pView->OnCmdMsg(nID, nCode, pExtra, pHandlerInfo))<br /> return TRUE;<br /> // 由框架处理该消息，CWnd没有覆盖OnCmdMsg，调用CCmdTarget::OnCmdMsg<br /> if (CWnd::OnCmdMsg(nID, nCode, pExtra, pHandlerInfo))<br /> return TRUE;<br /> // 将消息传递给应用程序，CWinApp没有覆盖OnCmdMsg，所以调用CCmdTarget::OnCmdTarget<br /> CWinApp* pApp = AfxGetApp();<br /> if (pApp != NULL && pApp->OnCmdMsg(nID, nCode, pExtra, pHandlerInfo))<br /> return TRUE;<br /> return FALSE;<br /> }<br /> // viewcore.cpp 154<br /> BOOL CView::OnCmdMsg(UINT nID, int nCode, void* pExtra,<br /> AFX_CMDHANDLERINFO* pHandlerInfo)<br /> {<br /> // 首先由活动视图处理该消息，调用CCmdTarget::OnCmdMsg<br /> if (CWnd::OnCmdMsg(nID, nCode, pExtra, pHandlerInfo))<br /> return TRUE;<br /> // then pump through document<br /> if (m_pDocument != NULL)<br /> {<br /> // 将该消息传递给视图对应的文档，调用CDocument::OnCmdMsg<br /> CPushRoutingView push(this);<br /> return m_pDocument->OnCmdMsg(nID, nCode, pExtra, pHandlerInfo);<br /> }<br /> return FALSE;<br /> }<br /> // doccore.cpp 834<br /> BOOL CDocument::OnCmdMsg(UINT nID, int nCode, void* pExtra,<br /> AFX_CMDHANDLERINFO* pHandlerInfo)<br /> {<br /> if (CCmdTarget::OnCmdMsg(nID, nCode, pExtra, pHandlerInfo))<br /> return TRUE;<br /> // otherwise check template，调用CDocTemplate::OnCmdMsg<br /> if (m_pDocTemplate != NULL &&<br /> m_pDocTemplate->OnCmdMsg(nID, nCode, pExtra, pHandlerInfo))<br /> return TRUE;<br /> return FALSE;<br /> }<br /> // doctempl.cpp 370<br /> BOOL CDocTemplate::OnCmdMsg(UINT nID, int nCode, void* pExtra,<br /> AFX_CMDHANDLERINFO* pHandlerInfo)<br /> {<br /> BOOL bReturn;<br /> CCmdTarget* pFactory = DYNAMIC_DOWNCAST(CCmdTarget, m_pAttachedFactory);<br /> if (nCode == CN_OLE_UNREGISTER && pFactory != NULL)<br /> bReturn = pFactory->OnCmdMsg(nID, nCode, pExtra, pHandlerInfo);<br /> else<br /> bReturn = CCmdTarget::OnCmdMsg(nID, nCode, pExtra, pHandlerInfo);<br /> return bReturn;<br /> }<br />  

上面的一些函数确定了程序执行流程，最终会调用到CCmdTarget::OnCmdMsg，该函数通过查找消息映射表，进而调用到消息处理函数。

// cmdtarg.cpp 297<br /> BOOL CCmdTarget::OnCmdMsg(UINT nID, int nCode, void* pExtra,<br /> AFX_CMDHANDLERINFO* pHandlerInfo)<br /> {<br /> // ...<br /> // determine the message number and code (packed into nCode)<br /> const AFX_MSGMAP* pMessageMap;<br /> const AFX_MSGMAP_ENTRY* lpEntry;<br /> UINT nMsg = 0;<br /> //...<br /> if (nCode != CN_UPDATE_COMMAND_UI)<br /> {<br /> nMsg = HIWORD(nCode);<br /> nCode = LOWORD(nCode);<br /> }<br /> //...<br /> // for backward compatibility HIWORD(nCode)==0 is WM_COMMAND<br /> if (nMsg == 0)<br /> nMsg = WM_COMMAND;<br /> // look through message map to see if it applies to us<br /> for (pMessageMap = GetMessageMap(); pMessageMap->pfnGetBaseMap != NULL;<br /> pMessageMap = (*pMessageMap->pfnGetBaseMap)())<br /> {<br /> // Note: catches BEGIN_MESSAGE_MAP(CMyClass, CMyClass)!<br /> ASSERT(pMessageMap != (*pMessageMap->pfnGetBaseMap)());<br /> lpEntry = AfxFindMessageEntry(pMessageMap->lpEntries, nMsg, nCode, nID);<br /> if (lpEntry != NULL)<br /> {<br /> // found it<br /> return _AfxDispatchCmdMsg(this, nID, nCode,<br /> lpEntry->pfn, pExtra, lpEntry->nSig, pHandlerInfo);<br /> }<br /> }<br /> return FALSE; // not handled<br /> }<br />