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软采用了所谓的消息映射机制，来完成不同对象之间消息的传递，本文就MFC9.0源码进行分析，大致讲解MFC的消息映射机制。
步入正题，在AfxWinMain() 函数中，当MFC框架初始化完成后，即 pThread->InitInstance() 执行完成，就开始进行消息循环，入口函数是pThread->Run()：
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1. // Perform specific initializations
2. if (!pThread->InitInstance())// MFC初始化框架 3. {
4. if (pThread->m_pMainWnd != NULL) 5. {
6. TRACE(traceAppMsg, 0, \);
7. pThread->m_pMainWnd->DestroyWindow(); 8. }
9. nReturnCode = pThread->ExitInstance(); 10. goto InitFailure; 11. }
12. nReturnCode = pThread->Run();// 进入消息循环
执行CWinApp:: Run():
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1. // Main running routine until application exits 2. int CWinApp::Run() 3. {
4. if (m_pMainWnd == NULL && AfxOleGetUserCtrl()) 5. {
6. // Not launched /Embedding or /Automation, but has no main window! 7. TRACE(traceAppMsg, 0, \ quitting application.\\n\); 8. AfxPostQuitMessage(0); 9. }
10. return CWinThread::Run(); 11. }
执行CWinThread::Run():
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1. // main running routine until thread exits 2. int CWinThread::Run() 3. {
4. ASSERT_VALID(this);
5. _AFX_THREAD_STATE* pState = AfxGetThreadState(); 6.
7. // for tracking the idle time state 8. BOOL bIdle = TRUE; 9. LONG lIdleCount = 0; 10.
11. // acquire and dispatch messages until a WM_QUIT message is received. 12. GetMessage:从系统获取消息，将消息从系统中移除，属于阻塞函数。当系统无消
息时，GetMessage会等待下一条消息。而函数PeekMesssge是以查看的方式从系统中获取消息，可以不将消息从系统中移除，是非阻塞函数；当系统无消息时，返回FALSE，继续执行后续代码
13. for (;;) 14. {
15. // phase1: check to see if we can do idle work 16. while (bIdle &&
17. !::PeekMessage(&(pState->m_msgCur), NULL, NULL, NULL, PM_NOREMOV
E)) 18. {
19. // call OnIdle while in bIdle state 20. if (!OnIdle(lIdleCount++))
21. bIdle = FALSE; // assume \ 22. } 23.
24. // phase2: pump messages while available 25. do 26. {
27. // pump message, but quit on WM_QUIT 28. if (!PumpMessage()) 29. return ExitInstance(); 30.
31. // reset \ 32. //if (IsIdleMessage(&m_msgCur))
33. if (IsIdleMessage(&(pState->m_msgCur))) 34. {
35. bIdle = TRUE; 36. lIdleCount = 0; 37. } 38.
39. } while (::PeekMessage(&(pState->m_msgCur), NULL, NULL, NULL, PM_NOR
EMOVE)); //查看消息队列中是否有消息
40. } 41. }
在 do-while 循环中进行消息的路由，主要函数就是 PumpMessage()，我们跟着进入这个函数看看做了什么：
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1. BOOL CWinThread::PumpMessage() 2. {
3. return AfxInternalPumpMessage(); 4. }
继续跟踪：
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1. BOOL AFXAPI AfxInternalPumpMessage() 2. {
3. _AFX_THREAD_STATE *pState = AfxGetThreadState(); 4.
5. if (!::GetMessage(&(pState->m_msgCur), NULL, NULL, NULL))// 从消息队列获
取消息 6. {
7. #ifdef _DEBUG
8. TRACE(traceAppMsg, 1, \
\);
9. pState->m_nDisablePumpCount++; // application must die 10. #endif
11. // Note: prevents calling message loop things in 'ExitInstance' 12. // will never be decremented 13. return FALSE; 14. } 15.
16. #ifdef _DEBUG
17. if (pState->m_nDisablePumpCount != 0) 18. {
19. TRACE(traceAppMsg, 0, \
permitted.\\n\); 20. ASSERT(FALSE); 21. }
22. #endif 23.
24. #ifdef _DEBUG
25. _AfxTraceMsg(_T(\), &(pState->m_msgCur)); 26. #endif 27.
28. // process this message 29.
30. if (pState->m_msgCur.message != WM_KICKIDLE && !AfxPreTranslateMessage(&
(pState->m_msgCur))) 31. {
32. ::TranslateMessage(&(pState->m_msgCur)); 33. ::DispatchMessage(&(pState->m_msgCur)); 34. }
35. return TRUE; 36. }
从上面的代码我们可以看到 MFC是通过 GetMessage() 来获取消息，然后再看下面这几句代码：
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1. if (pState->m_msgCur.message != WM_KICKIDLE && !AfxPreTranslateMessage(&(pSt
ate->m_msgCur))) 2. {
3. ::TranslateMessage(&(pState->m_msgCur)); 4. ::DispatchMessage(&(pState->m_msgCur)); 5. }
也就是说当系统获取消息后，先调用 AfxPreTranslateMessage() 这个看起来跟我们经常看到的PreTranslateMessage() 很像！我们来看看到底发生了什么：
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1. BOOL __cdecl AfxPreTranslateMessage(MSG* pMsg) 2. {
3. CWinThread *pThread = AfxGetThread(); 4. if( pThread )
5. return pThread->PreTranslateMessage( pMsg ); 6. else
7. return AfxInternalPreTranslateMessage( pMsg ); 8. }
执行 pThread->PreTranslateMessage()：
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1. BOOL CWinThread::PreTranslateMessage(MSG* pMsg) 2. {
3. ASSERT_VALID(this);
4. return AfxInternalPreTranslateMessage( pMsg ); 5. }
执行AfxInternalPreTranslateMessage():
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1. BOOL AfxInternalPreTranslateMessage(MSG* pMsg) 2. {
3. // ASSERT_VALID(this); 4.
5. CWinThread *pThread = AfxGetThread(); 6. if( pThread ) 7. {
8. // if this is a thread-message, short-circuit this function 9. if (pMsg->hwnd == NULL && pThread->DispatchThreadMessageEx(pMsg)) 10. return TRUE; 11. } 12.
13. // walk from target to main window 14. CWnd* pMainWnd = AfxGetMainWnd();
15. if (CWnd::WalkPreTranslateTree(pMainWnd->GetSafeHwnd(), pMsg))// 注意这个
函数
16. return TRUE; 17.
18. // in case of modeless dialogs, last chance route through main 19. // window's accelerator table 20. if (pMainWnd != NULL) 21. {
22. CWnd* pWnd = CWnd::FromHandle(pMsg->hwnd); 23. if (pWnd->GetTopLevelParent() != pMainWnd) 24. return pMainWnd->PreTranslateMessage(pMsg); 25. } 26.
27. return FALSE; // no special processing 28. }