RichTextBox中用指定字体和颜色高亮显示指定字符

using System;
using System.Windows.Forms;
using System.Text.RegularExpressions;
namespace RichTextBox描红指定内容
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.btnColor.Click += new EventHandler(BtnColor_Click);
            this.btnStart.Click += new EventHandler(BtnStart_Click);
            this.textBox2.Click += new EventHandler(TextBox_Click);
        }

        /// <summary>
        /// 选择颜色后，将按钮背景色设置成选中的色
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void BtnColor_Click(object sender, EventArgs e)
        {
            if (colorDialog1.ShowDialog() == DialogResult.OK)
            {
                btnColor.BackColor = colorDialog1.Color;
            }
        }

        private int temp = 0;
        private void BtnStart_Click(object sender, EventArgs e)
        {
            string key = textBox1.Text.Trim();
            string content = richTextBox1.Text.Trim();
            if (richTextBox1.Text.Trim() != "")
            {
                Regex re = new Regex(key);
               MatchCollection m = re.Matches(richTextBox1.Text, temp);
               foreach (Match sm in m)
               {
                   richTextBox1.Select(sm.Index, key.Length);
                   richTextBox1.SelectionColor = colorDialog1.Color;
                   richTextBox1.SelectionFont = fontDialog1.Font;
               }
            }
        }

        private void TextBox_Click(object sender, EventArgs e)
        {
            if (fontDialog1.ShowDialog() == DialogResult.OK)
            {
                textBox2.Text = fontDialog1.Font.ToString();
            }
        }
    }
}