如何为datagridview加上序号

using System;using System.Text;using System.Windows.Forms;using System.Drawing;namespace Test{    class DataGridViewEx : DataGridView    {        SolidBrush solidBrush;        public DataGridViewEx()        {            solidBrush = new SolidBrush(this.RowHeadersDefaultCellStyle.ForeColor);        }        protected override void OnRowPostPaint(DataGridViewRowPostPaintEventArgs e)        {            e.Graphics.DrawString((e.RowIndex + 1).ToString(), e.InheritedRowStyle.Font, solidBrush, e.RowBounds.Location.X + 15, e.RowBounds.Location.Y + 5); base.OnRowPostPaint(e);        }    }}