如何清空DC的内容?

[feng0hua0]

IntPtr dc1 = CreateDC("DISPLAY", null, null, (IntPtr)null);
//创建显示器的DC
g = Graphics.FromHdc(dc1);

在这里创建了一个显示器的DC,请问在屏幕上绘制了图形之后,如何清空DC的内容,就是把屏幕还原到DC创建之前的状态.

[cppfaq]

适时save，然后restore:

IntPtr dc1 = CreateDC("DISPLAY", null, null, (IntPtr) null);
            //创建显示器的DC
            Graphics g = Graphics.FromHdc(dc1);
            GraphicsState savePoint = g.Save();

            //绘制图形
            g.DrawLine(Pens.Blue, 0, 100, 200, 300);

            //还原到绘制前的状态
            g.Restore(savePoint);

[feng0hua0]

        GraphicsState saveDC;//设置为全局变量
        
        private void Form1_Load(object sender, EventArgs e)
        {
            IntPtr dc1 = CreateDC("DISPLAY", null, null, (IntPtr)null);
            g = Graphics.FromHdc(dc1);
            saveDC = g.Save();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            g.DrawLine(Pens.Blue, 0, 100, 200, 300);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            g.Restore(saveDC);
        }

按下BUTTON1后会绘制直线,但是在按下BUTTON2的时候,屏幕上的直线还是没有被清空,是不是少了哪个步骤?..
谢谢.