Create和CreateEx 区别

先来看CreateEx函数：

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，这两个重载函数的实现原理是让第一个函数调用了第二个函数。在第二个CreateEx中实际是通过调用Win32 SDK平台的ateWindowEx（CWnd没有此函数）来创建窗口的。

再来看Create函数：

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);
}

注意这两行：

 ASSERT(pParentWnd != NULL);
 ASSERT((dwStyle & WS_POPUP) == 0);  // 该行说明Create函数不允许窗口风格为WS_POPUP

可以看到，在Create函数之中又调用了CreateEx的第二个重载版本。

总结：

归根到底，MFC是通过CreateEx函数调用CreateWindowEx函数来创建窗口的。

注意一点：这个新创建的窗口是如何与我们的窗口对象进行绑定的呢？看第二个CreateEx的return上面的那一行：

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

在这里这只是进行判断。看它的注释：// should have been set in send msg hook

奥，它说在

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

处设置了m_hWnd的值。