我想请问一下,我在panel中画线,为什么没有显示。在其他程序中却能显示。 
           Graphics g;
            g = panel1.CreateGraphics();            
            Point p1, p2, p3;
            p1 = new Point(28, 60);
            p2 = new Point(185, 60);
            p3 = new Point(386, 120);
            Pen pen = new Pen(Color.Black);
            g.DrawLine(pen, p1, p2);
            g.DrawLine(pen, p2, p3);