RECT& rect, CMDIFrameWnd* pParentWnd,

       CCreateContext* pContext)

{

       if (pParentWnd == NULL)

       {

              CWnd* pMainWnd = AfxGetThread()->m_pMainWnd;

              ASSERT(pMainWnd != NULL);

              ASSERT_KINDOF(CMDIFrameWnd, pMainWnd);

              pParentWnd = (CMDIFrameWnd*)pMainWnd;

       }

    ……

       pParentWnd->RecalcLayout();



       CREATESTRUCT cs;

……

//指定了所属的MDI子窗口

       cs.hwndParent = pParentWnd->m_hWnd;

    ……

       cs.lpCreateParams = (LPVOID)pContext;



       if (!PreCreateWindow(cs))

       {

              PostNcDestroy();

              return FALSE;

       }

       MDICREATESTRUCT mcs;

    ……

       mcs.style = cs.style & ~(WS_MAXIMIZE | WS_VISIBLE);

       mcs.lParam = (LONG)cs.lpCreateParams;



       AfxHookWindowCreate(this);

    //发送WM_MDICREATE消息，创建了MDI子窗口

       HWND hWnd = (HWND)::SendMessage(pParentWnd->m_hWndMDIClient,

              WM_MDICREATE, 0, (LPARAM)&mcs);

       if (!AfxUnhookWindowCreate())

              PostNcDestroy();        // cleanup if MDICREATE fails too soon

    ……

       return TRUE;

}

当MDI子窗口创建了以后，MDI主窗口就可以用自己的函数实现对子窗口的管理，例如取得当前的活动子窗口是通过发送WM_MDIGETACTIVE消息实现的