如何在扩展的RichTextBox控件中添加表格功能？

using System;
using System.Windows.Forms;

namespace ExtendedRichTextBoxExample
{
    public partial class ExtendedRichTextBox : RichTextBox
    {
        public ExtendedRichTextBox()
        {
            InitializeComponent();
        }

        private void InsertTable()
        {
            // 弹出对话框，获取用户输入的行数和列数
            TableInputDialog dialog = new TableInputDialog();
            if (dialog.ShowDialog() == DialogResult.OK)
            {
                int rows = dialog.Rows;
                int columns = dialog.Columns;

                // 生成表格的HTML代码
                string tableHtml = "<table>";
                for (int i = 0; i < rows; i++)
                {
                    tableHtml += "<tr>";
                    for (int j = 0; j < columns; j++)
                    {
                        tableHtml += "<td> </td>";
                    }
                    tableHtml += "</tr>";
                }
                tableHtml += "</table>";

                // 将表格插入到RichTextBox中
                this.SelectedRtf = tableHtml;
            }
        }
    }
}