C#简单画图

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 KeyPress
{
    public partial class Form1 : Form
    {
        bool shouldPaint = false;

        public Form1()
        {
            InitializeComponent();
            //事件必须在构造函数中先添加事件句柄
            //声明了三个鼠标事件
            this.MouseDown += new MouseEventHandler(Form1_MouseDown);
            this.MouseUp += new MouseEventHandler(Form1_MouseUp);
            this.MouseMove+=new MouseEventHandler(Form1_MouseMove);
        }

        void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            shouldPaint = false;
        }

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            shouldPaint = true;
        }
        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (shouldPaint)
            {
                Graphics g = CreateGraphics();
                g.FillEllipse(
                    new SolidBrush(Color.BlueViolet),
                    e.X,e.Y,4,4);
                g.Dispose();
            }
        }
    }
}