C#实现红绿灯

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Drawing2D;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        private string strColor;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            g.FillRectangle(Brushes.White, this.ClientRectangle);
            //report dimensions of clipping rectangle to console
            Console.WriteLine("e.ClipRectangle = " + e.ClipRectangle);
            //draw outline
            g.FillRectangle(Brushes.Black,10,10,50,150);
            g.DrawEllipse(Pens.White,15,15,40,40);
            g.DrawEllipse(Pens.White,15,60,40,40);
            g.DrawEllipse(Pens.White,15,105,40,40);
            //use application state to draw exactly one of three lights
            switch(strColor)
            {
                case "red":
                    g.FillEllipse(Brushes.Red,15,15,40,40);
                    break;
                case "yellow":
                    g.FillEllipse(Brushes.Yellow,15,60,40,40);
                    break;
                case "green":
                    g.FillEllipse(Brushes.Green,15,105,40,40);
                    break;
                default:
                    g.FillEllipse(Brushes.Red,15,15,40,40);
                    break;
            }
                }

        private void Form1_Click(object sender, EventArgs e)
        {
            //change application state by altering value of strColor
            switch(strColor)
            {
                case "red":
                    strColor = "yellow";
                    break;
                case "yellow":
                    strColor = "green";
                    break;
                default:
                    strColor = "red";
                    break;
            }
            //invaliate the region containing the traffics lights
            this.Invalidate(new Rectangle(10, 10, 50, 150));
            //request an update
            this.Update();
        }
   }
}