让DataGridView显示行号

private void dataGridView1_RowPostPaint(object sender, DataGridViewRowPostPaintEventArgs e)
        ...{
            Rectangle rectangle = new Rectangle(e.RowBounds.Location.X,
                e.RowBounds.Location.Y,
                dataGridView1.RowHeadersWidth - 4,
                e.RowBounds.Height);

            TextRenderer.DrawText(e.Graphics, (e.RowIndex + 1).ToString(), 
                dataGridView1.RowHeadersDefaultCellStyle.Font,
                rectangle,
                dataGridView1.RowHeadersDefaultCellStyle.ForeColor, 
                TextFormatFlags.VerticalCenter | TextFormatFlags.Right);
        }