在屏幕上画图的C＃实现代码

DllImport所在的名字空间 using System.Runtime.InteropServices;
[DllImport("User32.dll")]
        public extern static System.IntPtr GetDC(System.IntPtr hWnd);   
        private void button19_Click(object sender, EventArgs e)
         {
             System.IntPtr    DesktopHandle   =    GetDC(System.IntPtr.Zero);
             Graphics g = Graphics.fromHdc(DesktopHandle);
             g.DrawRectangle(new Pen(Color.Red),new Rectangle(10,10,100,100));
         }