Winform 动态 画图 不闪

　　一、问题：解决winform动态画图闪的问题，网上搜的方法，大部分都是：

1. “this.SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.AllPaintingInWmPaint, true);”，甚至直接“this.DoubleBuffered = true;”。
2. 先 new 个Bitmap，画在Bitmap上，然后再把Bitmap画在界面上。

　　凡是直接这么给人解答问题的，基本都是属于道听途说，自己没试过的。或者根本就没注意要解决的是“动态”的问题。

　　二、解决方法：动态画图不闪的方法如下,先上效果图（请忽略鼠标样式，是gif录制软件的效果）：

　　

　　三、代码：简单封了个自定义控件，用Action传入画图方法：

 // --------------------------------------------------------------------------------------------------------------------
 // <copyright file="PictureBoxEx.cs" company="hyl">
 //   hyl
 // </copyright>
 // <summary>
 //   用Action传画图方法。不闪。
 // </summary>
 // --------------------------------------------------------------------------------------------------------------------

 namespace HYL
 {
     using System;
     using System.Drawing;
     using System.Windows.Forms;

     public partial class PictureBoxEx : PictureBox
     {
         /// <summary>
         /// 画图方法
         /// </summary>
         private Action<Graphics> draw;

         public PictureBoxEx()
         {
             this.InitializeComponent();

             // 开双缓存（用这种方法，画图不太复杂的话，甚至不开也不闪。。。）
             this.SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.AllPaintingInWmPaint, true);
         }

         public void Rander(Action<Graphics> Draw)
         {
             this.Invalidate();
             this.draw = Draw;
         }

         protected override void OnPaint(PaintEventArgs pe)
         {
             base.OnPaint(pe);

             // 画图
             this.draw?.Invoke(pe.Graphics);
         }
     }
 }

　　重点在于要在 “OnPaint” 执行画图代码，也就是说要用 “OnPaint” 里的 “pe.Graphics” 来画。

　　四、调用的方式如下：

 namespace HYL
 {
     using System;
     using System.Collections.Generic;
     using System.Drawing;
     using System.Linq;
     using System.Windows.Forms;

     public partial class Form1 : Form
     {
         List<Line> lines = new List<Line>();

         private bool painting;

         public Form1()
         {
             this.InitializeComponent();
         }

         private void panel1_MouseDown(object sender, MouseEventArgs e)
         {
             if (e.Button == MouseButtons.Left)
             {
                 // 左键确定点
                 if (this.btnLine.Checked)
                 {
                     this.lines.Last().Points.Add(new LinePoint { IsTemp = false, Point = e.Location });
                     this.painting = true;
                 }
             }

             if (e.Button == MouseButtons.Right)
             {
                 // 右键停止画图
                 if (this.btnLine.Checked)
                 {
                     this.ClearEmptyLines();
                 }

                 this.painting = false;
                 this.btnLine.Checked = false;
             }
         }

         private void ClearEmptyLines()
         {
             this.lines = this.lines.Where(l => l.Points.Count > ).ToList();
             if (this.lines.Count > )
             {
                 var lastLine = this.lines.Last();
                 lastLine.ClearTempPoints();
             }
         }

         private void panel1_MouseMove(object sender, MouseEventArgs e)
         {
             if (this.painting)
             {
                 if (this.btnLine.Checked)
                 {
                     this.PaintingLine(e);
                 }

                 this.Draw();
             }
         }

         private void PaintingLine(MouseEventArgs e)
         {
             var lastLine = this.lines.Last();
             var lastPoint = lastLine.Points.Last();

             if (lastPoint.IsTemp)
             {
                 lastLine.Points.Remove(lastPoint);
             }

             LinePoint newPoint = new LinePoint { IsTemp = true, Point = e.Location };
             lastLine.Points.Add(newPoint);
         }

         /// <summary>
         /// 画图
         /// </summary>
         private void Draw()
         {
             Action<Graphics> draw = g =>
                 {
                     Pen pen = new Pen(Color.Black, );
                     g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                     g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;

                     if (this.lines != null)
                     {
                         foreach (Line line in this.lines)
                         {
                             g.DrawLines(pen, line.GetPoints().ToArray());
                         }
                     }
                 };

             this.pictureBoxEx1.Rander(draw);
         }

         private void btnLine_CheckedChanged(object sender, EventArgs e)
         {
             if (this.btnLine.Checked)
             {
                 this.lines.Add(new Line());
             }
             else
             {
                 this.ClearEmptyLines();
                 this.painting = false;
                 this.Draw();
             }
         }
     }

     public class Line : ShapeElement
     {
         public Line()
         {
             this.Points = new List<LinePoint>();
         }

         // 线里的点
         public IList<LinePoint> Points { get; set; }

         // 获取Point的集合
         public IList<Point> GetPoints()
         {
             return this.Points.Select(p => p.Point).ToList();
         }

         // 清理临时点
         public void ClearTempPoints()
         {
             this.Points = this.Points.Where(p => !p.IsTemp).ToList();
         }
     }

     public class LinePoint
     {
         public Point Point { get; set; }

         // 是否临时点
         public bool IsTemp { get; set; }
     }
 }