using System;using System.Collections.Generic;using System.Drawing;using System.Windows.Forms;namespace WindowsFormsapplication2{    //http://bbs.csdn.net/topics/390567044    //http://heisetoufa.iteye.com/blog/380977    //http://blog.csdn.net/xuyongbeijing2008/article/details/17371311    public partial class Form2 : Form    {        bool bDrawStart = false;        Point pointStart = Point.Empty;        Point pointContinue = Point.Empty;        Dictionary<Point, Point> dicPoints;        public Form2()        {            InitializeComponent();            dicPoints = new Dictionary<Point, Point>();            DoubleBuffered = true;            this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.OptimizedDoubleBuffer | ControlStyles.UserPaint, true);            this.MouseDown += new MouseEventHandler(frmMain_MouseDown);            this.MouseMove += new MouseEventHandler(frmMain_MouseMove);            this.MouseUp += new MouseEventHandler(frmMain_MouseUp);            this.Paint += new PaintEventHandler(frmMain_Paint);        }        PRivate void frmMain_Paint(object sender, PaintEventArgs e)        {            Pen pen = new Pen(Color.Black, 1f);            pen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dash;                        if (bDrawStart)            {                //實時的畫矩形                int w = pointContinue.X - pointStart.X;                int h = pointContinue.Y - pointStart.Y;                Rectangle rect = new Rectangle(pointStart, new Size(w, h));                e.Graphics.DrawRectangle(pen, rect);            }            pen.Dispose();        }        void frmMain_MouseDown(object sender, MouseEventArgs e)        {            if (bDrawStart)            {                bDrawStart = false;            }            else            {                bDrawStart = true;                pointStart = e.Location;            }        }        void frmMain_MouseMove(object sender, MouseEventArgs e)        {            if (bDrawStart)            {                pointContinue = e.Location;                //Refresh();                Invalidate();            }        }        void frmMain_MouseUp(object sender, MouseEventArgs e)        {            if (bDrawStart)            {                dicPoints.Add(pointStart, pointContinue);            }            bDrawStart = false;        }        //...    }}