让DataGridView显示行号

 private void dataGridView1_RowPostPaint(object sender, DataGridViewRowPostPaintEventArgs e)
        {
            for (int i = 0; i < dataGridView1.Rows.Count; i++)
            {
                if (Convert.ToDouble(dataGridView1.Rows[i].Cells["E"].Value) > (double)numericUpDown1.Value || Convert.ToDouble(dataGridView1.Rows[i].Cells["E"].Value) < -(double)numericUpDown1.Value)
                {
                   dataGridView1.Rows[i].Cells["E"].Style.BackColor = Color.SkyBlue;
                }
            }
             #region 让DataGridView显示行号
           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);
            #endregion
        }