這兩天都在看RichTextBox行號問題，發現網上的實現方式都有各種各樣的問題
要麼是 對齊不準，要麼是閃爍，要麼滾動條繫結有問題
結合各篇文章最後 就寫了一個相對完美解決方案

效果圖

思路：
1.新建控制元件繼承自RichTextBox
2.設定SelectionIndent 使這個現實區域向右移動
3.在移動出來的空白區域顯示一個panl 使用Graphics 繪圖 繪製行號內容
4.繫結繪製事件到 OnTextChanged OnVScroll

閃爍問題解決：
首先使用雙緩衝技術，發現還是閃爍
最終使用的方案是 先在一張圖上繪製，繪製完畢之後 把圖繪到空白區域

最終原始碼：

public class AdaScrollRichTextBox:RichTextBox
    {
        Panel panel1;
        public AdaScrollRichTextBox()
        {
            InitializeLineId();
        }

        private void InitializeLineId()
        {
            this.SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.ResizeRedraw
 
 | ControlStyles.AllPaintingInWmPaint, true);
            this.panel1 = new Panel();
            this.panel1.Font = new System.Drawing.Font("宋體", 14F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(134)));
            this.panel1.Width = 35;
            this.panel1.Dock
 
 = DockStyle.Left;
            this.panel1.BackColor = System.Drawing.Color.FromArgb(((int)(((byte)(5)))), ((int)(((byte)(5)))), ((int)(((byte)(5)))));
            this.SelectionIndent = 35;
            this.Controls.Add(this.panel1);Controls。
        }
        public void showLineNo()
        {
            this.SelectionIndent = 35;
            Point p = this.Location;
            int crntFirstIndex = this.GetCharIndexFromPosition(p);

            int crntFirstLine = this.GetLineFromCharIndex(crntFirstIndex);

            Point crntFirstPos = this.GetPositionFromCharIndex(crntFirstIndex);

            p.Y += this.Height;

            int crntLastIndex = this.GetCharIndexFromPosition(p);

            int crntLastLine = this.GetLineFromCharIndex(crntLastIndex);
            Point crntLastPos = this.GetPositionFromCharIndex(crntLastIndex);

            //準備畫圖
            Graphics g = this.panel1.CreateGraphics();
            //新建圖，之後的繪製在圖上進行，繪製完畢之後繪製到g上
            Bitmap bufferimage = new Bitmap(this.panel1.Width, this.panel1.Height);
            Graphics g1 = Graphics.FromImage(bufferimage);
            g1.Clear(this.BackColor);
            g1.SmoothingMode = SmoothingMode.HighQuality; //高質量
            g1.PixelOffsetMode = PixelOffsetMode.HighQuality; //高畫素偏移質量

            Font font = new Font(this.Font, this.Font.Style);

            SolidBrush brush = new SolidBrush(Color.Green);

            //畫圖開始



            Rectangle rect = this.panel1.ClientRectangle;
            brush.Color = this.panel1.BackColor;

            g1.FillRectangle(brush, 0, 0, this.panel1.ClientRectangle.Width, this.panel1.ClientRectangle.Height);

            brush.Color = Color.Green;

            //繪製行號

            int lineSpace = 0;

            if (crntFirstLine != crntLastLine)
            {
                lineSpace = (crntLastPos.Y - crntFirstPos.Y) / (crntLastLine - crntFirstLine);

            }

            else
            {
                lineSpace = Convert.ToInt32(this.Font.Size);

            }

            //這裡2.6引數可以按程式碼實際修改
            int brushX = this.panel1.ClientRectangle.Width - Convert.ToInt32(font.Size * 2.6);
            //這裡0.1引數可以按程式碼實際修改
            int brushY = crntLastPos.Y + Convert.ToInt32(font.Size * 0.1f);
            for (int i = crntLastLine; i >= crntFirstLine; i--)
            {

                g1.DrawString((i + 1).ToString(), font, brush, brushX, brushY);

                brushY -= lineSpace;
            }
            g.DrawImage(bufferimage, 0, 0);

            g1.Dispose();
            g.Dispose();
            font.Dispose();
            brush.Dispose();

        }

        protected override void OnTextChanged(EventArgs e)
        {
            showLineNo();
            base.OnTextChanged(e);
        }
        protected override void OnVScroll(EventArgs e)
        {
            showLineNo();
            base.OnVScroll(e);
        }

    }