1. 捕获WM_NCHITTEST：

    UINT CMyDialog::OnNcHitTest(CPoint point)
    {
         UINT nResult = CDialog::OnNcHitTest(point);
         return nResult  == HTCLIENT ? HTCAPTION : nResult;
    }

2. 捕获WM_LBUTTONDOWN：
         
    void CMyDialog::OnLButtonDown(CPoint point)
    {
          SendMessage(WM_SYSCOMMAND, 0xF012, 0);
          CDialog::OnLButtonDown(point);
    }