如何限制mdi子框架最大化时的大小?

用ptMaxTrackSize代替prMaxSize,如下所示:

void CChildFrame::OnGetMinMaxInfo(MINMAXINFO FAR* lpMMI)
{
   // TODO: Add your message handler code here and/or call default
   CChildFrame::OnGetMinMaxInfo(lpMMI);
   lpMMI->ptMaxTrackSize.x = 300;
   lpMMI->ptMaxTrackSize.y = 400;
}