dataGridView画序号

private void dataGridView1_RowPostPaint(object sender, DataGridViewRowPostPaintEventArgs e)
{
SolidBrush b = new SolidBrush(this.datagv_det.RowHeadersDefaultCellStyle.ForeColor);
e.Graphics.DrawString((e.RowIndex + 1).ToString(System.Globalization.CultureInfo.CurrentUICulture), this.datagv_det.DefaultCellStyle.Font, b, e.RowBounds.Location.X + 20, e.RowBounds.Location.Y + 4);

}