C#画图

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;

namespace 事件
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private Graphics my;
        string pensColor = "Black";
       
        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            Rectangle re = new Rectangle();
            if (e.Button != MouseButtons.Left) return;

            re.X = e.X - 1;
            re.Y = e.Y - 1;
            re.Width = 4;
            re.Height = 4;
            
            switch (pensColor)
            {
                case "Green": my.DrawEllipse(System.Drawing.Pens.Green, re);
                    break;
                case "Red": my.DrawEllipse(System.Drawing.Pens.Red, re);
                    break;
                case "Blue": my.DrawEllipse(System.Drawing.Pens.Blue, re);
                    break;
                //case default() :break;
            }
            
        }

        private void draw(Color c)
        {
            
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            my = this.CreateGraphics();
        }

        private void button3_Click(object sender, EventArgs e)
        {
            pensColor = "Green";//button3.BackColor.ToString();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            pensColor = "Blue";//button2.BackColor.ToString();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            pensColor = "Red"; //button1.BackColor.ToString();
        }

        private void button4_Click(object sender, EventArgs e)
        {
            this.Refresh();
        }
    }
}

运行程序便可在窗体内进行画图，可去掉switch语句调用默认颜色进行画图操作！