think window procedure
作者：温昱
1. 用Win32 API编程时，window procedure比较明显，那就是程序员自定义window procedure，但Win32提供了一个API函数DefWindowProc()，缺省的处理要交给它。
int APIENTRY WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nCmdShow){WNDCLASSEX wcex;wcex.lpszClassName = "MyClass";wcex.lpfnWndProc = (WNDPROC)MyWndProc;...RegisterClassEx(&wcex);HWND hWnd;hWnd = CreateWindow("MyClass", szTitle, WS_OVERLAPPEDWINDOW,CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);if (!hWnd)return FALSE;ShowWindow(hWnd, nCmdShow);UpdateWindow(hWnd);while (GetMessage(&msg, NULL, 0, 0)) {TranslateMessage(&msg);DispatchMessage(&msg);}return msg.wParam;}LRESULT CALLBACK MyWndProc(HWND hWnd,UINT message, WPARAM wParam, LPARAM lParam){switch (message) {...default:return DefWindowProc(hWnd, message, wParam, lParam);}return 0;} 2. 用MFC，window procedure会复杂一些，先看静态的，就是MFC预注册过的那些类，一句话，MFC替你打点好了window procedure的事。 2.1 最抽象的，MFC把window procedure封装了起来，程序员只需"programming by difference"，你对哪个消息感兴趣，就建立哪个消息的响应函数。（当然还有虚函数override...）
void CMyClass::OnLButtonDown(UINT nFlags, CPoint pt){...} 2.2 往底层一点，我们可以说CWnd::WindowProc()是现在的window procedure，它是一个template method，被你"programming by difference"的消息，会被它交给CWnd::OnWndMsg()处理，缺省的，会被它交给CWnd::DefWindowProc()处理。当然，上面说的没有考虑多态的情况，其实CWnd::OnWndMsg()和CWnd::DefWindowProc()都是虚函数。我们也注意到CWnd::DefWindowProc()中调用了::DefWindowProc()，也就是Win32 API的DefWindowProc()。 class CWnd : public CCmdTarget{...protected:// for processing Windows messagesvirtual LRESULT WindowProc(UINT message, WPARAM wParam, LPARAM lParam);virtual BOOL OnWndMsg(UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult);...};///template methodLRESULT CWnd::WindowProc(UINT message, WPARAM wParam, LPARAM lParam){LRESULT lResult = 0;if (!OnWndMsg(message, wParam, lParam, &lResult))lResult = DefWindowProc(message, wParam, lParam);return lResult;}//primitive methodLRESULT CWnd::DefWindowProc(UINT nMsg, WPARAM wParam, LPARAM lParam){if (m_pfnSuper != NULL)return ::CallWindowProc(m_pfnSuper, m_hWnd, nMsg, wParam, lParam);...} 2.3 往更底层，来看看MFC预注册的那些类，window procedure是谁。注意，Pre-Registers Window Classes没有什么神秘的，因为Window Classes就是一个struct，而当你想用某个Pre-Registers Window Classes时，无非是传一个parameter过去，某段程序一判断，给wc结构赋值，调用AfxRegisterClass( & wc)，OK。哈哈，我看到了，用的还是Win32 API的::DefWindowProc()。 BOOL CWnd::CreateEx(DWORD dwExStyle, LPCTSTR lpszClassName,LPCTSTR lpszWindowName, DWORD dwStyle,int x, int y, int nWidth, int nHeight,HWND hWndParent, HMENU nIDorHMenu, LPVOID lpParam){CREATESTRUCT cs;cs.lpszClass = lpszClassName;...PreCreateWindow(cs); //########pass a cs with lpszClass null...}BOOL CWnd::PreCreateWindow(CREATESTRUCT& cs) //########pass a cs with lpszClass NULL{if (cs.lpszClass == NULL) //########pass a cs with lpszClass NULL{// make sure the default window class is registeredVERIFY(AfxDeferRegisterClass(AFX_WND_REG));//########pass a para AFX_WND_REG// no WNDCLASS provided - use child window defaultASSERT(cs.style & WS_CHILD);cs.lpszClass = _afxWnd;}return TRUE;}#define AfxDeferRegisterClass(fClass) AfxEndDeferRegisterClass(fClass)BOOL AFXAPI AfxEndDeferRegisterClass(LONG fToRegister)//########pass a para AFX_WND_REG{...// common initializationWNDCLASS wndcls;memset( & wndcls, 0, sizeof(WNDCLASS));wndcls.lpfnWndProc = DefWindowProc; //########## here,Win32 API ::DefWindowProc()wndcls.hInstance = AfxGetInstanceHandle();wndcls.hCursor = afxData.hcurArrow;...if (fToRegister & AFX_WND_REG) //########pass a para AFX_WND_REG{wndcls.st 
