给RichTextBox添加行号，且没有误差

【实例截图】

【核心代码】

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;

/*
 * 此测试程序的作用在于克服一下几个技术难点：
 * 1.在Richtextbox的旁边显示行号。
 * 2.可以使Richtextbox跳到指定行号的位置
 * 3.可以通过鼠标点击Richtextbox的某行以获取Richtextbox中该行的内容。
 * 以上几个技术主要应用在程序调试错误时，在Richtextbox中将出现错误提示信息，用户可以通过点击错误提示Richtextbox中的某行
 * 使得源代码编辑器中的Richtextbox直接跳到该行，方便用户修改程序。
 * */

namespace WindowsFormsApplication4
{
    public partial class Richtextbox测试 : Form
    {
        public Richtextbox测试()
        {
            InitializeComponent();
        }

        private void richTextBox1_TextChanged(object sender, EventArgs e)
        {
            panel1.Invalidate();
        }

        private void richTextBox1_VScroll(object sender, EventArgs e)
        {
            panel1.Invalidate();
        }

        private void panel1_Paint(object sender, PaintEventArgs e)
        {
            showLineNo();
        }

        private void showLineNo()

        {
            //获得当前坐标信息
            Point p = this.richTextBox1.Location;
            int crntFirstIndex = this.richTextBox1.GetCharIndexFromPosition(p);
            int crntFirstLine = this.richTextBox1.GetLineFromCharIndex(crntFirstIndex);
            Point crntFirstPos = this.richTextBox1.GetPositionFromCharIndex(crntFirstIndex);
            //
            p.Y  = this.richTextBox1.Height;
            int crntLastIndex = this.richTextBox1.GetCharIndexFromPosition(p);
            int crntLastLine = this.richTextBox1.GetLineFromCharIndex(crntLastIndex);
            Point crntLastPos = this.richTextBox1.GetPositionFromCharIndex(crntLastIndex);
             //准备画图
            Graphics g = this.panel1.CreateGraphics();
            Font font = new Font(this.richTextBox1.Font,this.richTextBox1.Font.Style);
            SolidBrush brush = new SolidBrush(Color.Green);

             //画图开始

             //刷新画布
            Rectangle rect = this.panel1.ClientRectangle;
            brush.Color = this.panel1.BackColor;
            g.FillRectangle(brush, 0, 0, this.panel1.ClientRectangle.Width,this.panel1.ClientRectangle.Height);
            brush.Color = Color.Green;//重置画笔颜色
             //绘制行号
            int lineSpace = 0;
            if (crntFirstLine != crntLastLine)
            {
                lineSpace = (crntLastPos.Y - crntFirstPos.Y) / (crntLastLine - crntFirstLine);
            }
            else
            {
                lineSpace =(int)( Convert.ToInt32(this.richTextBox1.Font.Size)*1.6 );
            }
            int brushX = this.panel1.ClientRectangle.Width - Convert.ToInt32(font.Size * 3);
            int brushY = crntLastPos.Y  Convert.ToInt32(font.Size*0.21f);
            for (int i = crntLastLine; i >= 0;i-- )
            {
                g.DrawString((i   1).ToString(), font, brush, brushX, brushY);
                brushY -= lineSpace;
            }
            g.Dispose();
            font.Dispose();
            brush.Dispose();
        }
        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            int lineNumber = Convert.ToInt32(textBox1.Text.Trim());
            int start=richTextBox1.GetFirstCharIndexFromLine(lineNumber-1);
            this.richTextBox1.SelectionStart = start;
            this.richTextBox1.ScrollToCaret();
        }

        private void richTextBox1_Click(object sender, EventArgs e)
        {
            
        }

        private void richTextBox1_MouseClick(object sender, MouseEventArgs e)
        {
            Point p = new Point(e.X,e.Y);
            int crntFirstIndex = this.richTextBox1.GetCharIndexFromPosition(p);
            int lineNumber =richTextBox1.GetLineFromCharIndex(crntFirstIndex);
            if(lineNumber<richTextBox1.Lines.Length)
                textBox2.Text=richTextBox1.Lines[lineNumber];
        }

    }
}