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This issue of the content of the editor will bring you about the window process function WindowProc and DefWindowProc function is how, the article is rich in content and professional analysis and description for you, after reading this article, I hope you can get something.

Window procedure functions-WindowProc and DefWindowProc functions in the Windows operating system, when the window is displayed, it can receive a steady stream of messages from the system, and then the window needs to process these messages, so you need a function to process these messages. In API, a function is defined as a callback function. When the system needs to send a message to the window, it will call the callback function WindowProc given by the window. If the WindowProc function does not process the message, it can be transferred to the DefWindowProc function to handle it, which is the default message handling function of the system. When you press the menu, or click on the window, the window needs to run this message handler. The function WindowProc is declared as follows: LRESULT CALLBACK WindowProc (HWND hwnd,hwnd is the handle to the current window. UMsg is a message sent by the system. WParam is a message parameter. LParam is a message parameter. This function must be a static function, that is, a global function, and the address has been determined at compile time. Because it needs to be set in the registered window type, it is as follows: line 15 of # 008 ATOM MyRegisterClass (HINSTANCE hInstance) is the message handler function of the setting window. The function DefWindowProc is declared as follows: LRESULT DefWindowProc (HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam); this function has the same arguments as the function above. It's just that it handles all default messages. An example of calling these two functions is as follows: line # 001 / / Line 8 defines the message handling function line 14 to start processing according to different messages. Lines 29 and 41 both call the DefWindowProc function to handle outstanding messages. With the window message handling function, you can respond to different messages and implement a variety of functions.

1. When programming with Win32 API, window procedure is more obvious, that is, programmers customize window procedure, but Win32 provides an API function DefWindowProc (), which is left to it by default.

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;}

two。 Using MFC,window procedure will be more complicated, first look at the static, that is, MFC pre-registered those classes, in a word, MFC for you to take care of window procedure.

2.1Abstract, MFC encapsulates window procedure. Programmers only need to "programming by difference" and set up a response function for any message you are interested in. (and of course the virtual function override...)

Void CMyClass::OnLButtonDown (UINT nFlags, CPoint pt) {...}

2.2 to the bottom, we can say that CWnd::WindowProc () is the current window procedure, it is a template method, the message that you "programming by difference" will be handed over to CWnd::OnWndMsg () for processing, and by default, it will be handed over to CWnd::DefWindowProc () for processing. Of course, the above does not consider the case of polymorphism, in fact, CWnd::OnWndMsg () and CWnd::DefWindowProc () are virtual functions. We also notice that CWnd::DefWindowProc () calls:: DefWindowProc (), that is, Win32.

DefWindowProc () for API.

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 LPARAM lParam 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);...}

Take a look at the classes pre-registered by MFC, who is window procedure. Note that there is nothing mysterious about Pre-Registers Window Classes, because Window Classes is a struct, and when you want to use a Pre-Registers Window Classes, all you have to do is pass a parameter, make a judgment, assign a value to the wc structure, and call AfxRegisterClass (& wc), OK. Haha, I see it. I still use Win32 API:: 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.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;wndcls.lpszClassName = _ afxWnd; / / # pass a para _ afxWndAfxRegisterClass (& wndcls) ...} const TCHAR _ afxWnd [] = AFX_WND;#define AFX_WND AFX_WNDCLASS ("Wnd") # define AFX_WNDCLASS (s)\ _ T ("Afx") _ T (s) _ T ("42") _ STATIC_SUFFIX _ UNICODE_SUFFIX _ DEBUG_SUFFIX

2.4 OK, let's sum up.

Class CWnd: public CCmdTarget {. Protected:virtual LRESULT WindowProc (UINT message, WPARAM wParam, LPARAM lParam); virtual BOOL OnWndMsg (UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult); virtual LRESULT DefWindowProc (UINT message, WPARAM wParam, LPARAM lParam); virtual BOOL OnCommand (WPARAM wParam, LPARAM lParam); virtual BOOL OnNotify (WPARAM wParam, LPARAM lParam, LRESULT* pResult);...} LRESULT CALLBACKAfxWndProc (HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam) {CWnd* pWnd = CWnd::FromHandlePermanent (hWnd); return AfxCallWndProc (pWnd, hWnd, nMsg, wParam, lParam) } LRESULT AFXAPIAfxCallWndProc (CWnd* pWnd, HWND hWnd, UINT nMsg,WPARAM wParam = 0, LPARAM lParam = 0) {LRESULT lResult;lResult = pWnd- > WindowProc (nMsg, wParam, lParam); return lResult;} LRESULT CWnd::WindowProc (UINT message, WPARAM wParam, LPARAM lParam) {LRESULT lResult = 0X if (! OnWndMsg (message, wParam, lParam, & lResult) lResult = DefWindowProc (message, wParam, lParam); return lResult;} BOOL CWnd::OnWndMsg (UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult) {if (message = WM_COMMAND) WM_COMMAND (OnCommand, OnCommand) Else if (message = = WM_NOTIFY) OnNotify (wParam, lParam, & lResult); else... / / msg map related} LRESULT CWnd::DefWindowProc (UINT nMsg, WPARAM wParam, LPARAM lParam) {if (m_pfnSuper! = NULL) return:: CallWindowProc (m_pfnSuper, m_hWnd, nMsg, wParam, lParam);} this is what the window procedure function WindowProc and DefWindowProc function shared by Xiaobian is like. If you happen to have similar doubts, please refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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