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 > 1).ToList();
            if (this.lines.Count > 0)
            {
                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, 2);
                    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; }
    }
}