利用Form()使绘图可以不消失

   1:          public Form1()

   2:          {

   3:              InitializeComponent();

   4:              this.Show();

   5:              Graphics grp = this.CreateGraphics();

   6:              Pen p = new Pen(Color.Black, 2);

   7:              grp.DrawLine(p, new Point(0, 0), new Point(100, 100));

   8:              grp.DrawEllipse(p,20,20,100,80);

   9:              //draw ellipse according responding rectangle.

  10:              grp.DrawRectangle(p, 20, 20, 100, 80);

  11:   

  12:          }