Create和CreateEx 區別

先來看CreateEx函數：

BOOL CWnd::CreateEx(DWORD dwExStyle, LPCTSTR lpszClassName,
  LPCTSTR lpszWindowName, DWORD dwStyle,
  const RECT& rect, CWnd* pParentWnd, UINT nID,
  LPVOID lpParam /* = NULL */)
{
 return CreateEx(dwExStyle, lpszClassName, lpszWindowName, dwStyle,
  rect.left, rect.top, rect.right - rect.left, rect.bottom - rect.top,
  pParentWnd->GetSafeHwnd(), (HMENU)nID, lpParam);
}

 

 

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)
{
 // allow modification of several common create parameters
 CREATESTRUCT cs;
 cs.dwExStyle = dwExStyle;
 cs.lpszClass = lpszClassName;
 cs.lpszName = lpszWindowName;
 cs.style = dwStyle;
 cs.x = x;
 cs.y = y;
 cs.cx = nWidth;
 cs.cy = nHeight;
 cs.hwndParent = hWndParent;
 cs.hMenu = nIDorHMenu;
 cs.hInstance = AfxGetInstanceHandle();
 cs.lpCreateParams = lpParam;

 if (!PreCreateWindow(cs))
 {
  PostNcDestroy();
  return FALSE;
 }

 AfxHookWindowCreate(this);
 HWND hWnd = ::CreateWindowEx(cs.dwExStyle, cs.lpszClass,
   cs.lpszName, cs.style, cs.x, cs.y, cs.cx, cs.cy,
   cs.hwndParent, cs.hMenu, cs.hInstance, cs.lpCreateParams);

#ifdef _DEBUG
 if (hWnd == NULL)
 {
  TRACE1("Warning: Window creation failed: GetLastError returns 0x%8.8X/n",
   GetLastError());
 }
#endif

 if (!AfxUnhookWindowCreate())
  PostNcDestroy();        // cleanup if CreateWindowEx fails too soon

 if (hWnd == NULL)
  return FALSE;
 ASSERT(hWnd == m_hWnd); // should have been set in send msg hook
 return TRUE;
}

可以看到，這兩個重載函數的實現原理是讓第一個函數調用了第二個函數。在第二個CreateEx中實際是通過調用Win32 SDK平台的ateWindowEx（CWnd沒有此函數）來建立視窗的。

 

再來看Create函數：

BOOL CWnd::Create(LPCTSTR lpszClassName,
 LPCTSTR lpszWindowName, DWORD dwStyle,
 const RECT& rect,
 CWnd* pParentWnd, UINT nID,
 CCreateContext* pContext)
{
 // can't use for desktop or pop-up windows (use CreateEx instead)
 ASSERT(pParentWnd != NULL);
 ASSERT((dwStyle & WS_POPUP) == 0);

 return CreateEx(0, lpszClassName, lpszWindowName,
  dwStyle | WS_CHILD,
  rect.left, rect.top,
  rect.right - rect.left, rect.bottom - rect.top,
  pParentWnd->GetSafeHwnd(), (HMENU)nID, (LPVOID)pContext);
}

注意這兩行：

 ASSERT(pParentWnd != NULL);
 ASSERT((dwStyle & WS_POPUP) == 0);  // 該行說明Create函數不允許視窗風格為WS_POPUP

可以看到，在Create函數之中又調用了CreateEx的第二個重載版本。

 

總結：

歸根到底，MFC是通過CreateEx函數調用CreateWindowEx函數來建立視窗的。

 

注意一點：這個新建立的視窗是如何與我們的視窗對象進行綁定的呢？看第二個CreateEx的return上面的那一行：

ASSERT(hWnd == m_hWnd); // should have been set in send msg hook

在這裡這隻是進行判斷。看它的注釋：// should have been set in send msg hook

奧，它說在

if (!AfxUnhookWindowCreate())
  PostNcDestroy();        // cleanup if CreateWindowEx fails too soon

處設定了m_hWnd的值。