窗口过程函数-----WindowProc和DefWindowProc函数[转]

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 messages
virtual LRESULT WindowProc(UINT message, WPARAM wParam, LPARAM lParam);
virtual BOOL OnWndMsg(UINT message, WPARAM wParam, LPARAM lParam, LRESULT* pResult);
...
};
///template method
LRESULT 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 method
LRESULT 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 registered
VERIFY(AfxDeferRegisterClass(AFX_WND_REG));//########pass a para AFX_WND_REG
// no WNDCLASS provided - use child window default
ASSERT(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 initialization
WNDCLASS 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 _afxWnd
AfxRegisterClass( & 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 好，总结一下。

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 CALLBACK
AfxWndProc(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam)
{
CWnd* pWnd = CWnd::FromHandlePermanent(hWnd);
return AfxCallWndProc(pWnd, hWnd, nMsg, wParam, lParam);
}
LRESULT AFXAPI
AfxCallWndProc(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 = 0;
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)
OnCommand(wParam, lParam);
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);
}