C#设置MDI子窗体不可移动

protected override void WndProc(ref Message m)
        {
            const int WM_NCLBUTTONDOWN = 161;
            const int WM_SYSCOMMAND = 274;
            const int HTCAPTION = 2;
            const int SC_MOVE = 61456;

            if ((m.Msg == WM_SYSCOMMAND) && (m.WParam.ToInt32() == SC_MOVE))
                return;

            if ((m.Msg == WM_NCLBUTTONDOWN) && (m.WParam.ToInt32() == HTCAPTION))
                return;

            base.WndProc(ref m);
        }