think window procedure

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);
}

(完)