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。
