为了表示行号，我们可以在DataGridView的RowPostPaint事件中进行绘制。RowPostPaint事件，具体可以参照MSDN。
下面是实现代码：
private void dataGridView1_RowPostPaint(object sender, DataGridViewRowPostPaintEventArgs e)
{
System.Drawing.Rectangle rectangle =
new System.Drawing.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);
}