C# DataGridView 合并相同的行

    private void dataGridView1_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
    {
        if (e.RowIndex >= 0 && e.ColumnIndex >= 0 && e.Value.ToString() != string.Empty)
        {
            #region
            int UpRows = 0;//上面相同的行数
            int DownRows = 0;//下面相同的行数
            int count = 0;//总行数
            int cellwidth = e.CellBounds.Width;//列宽
            //获取下面的行数
            for (int i = e.RowIndex; i < this.dataGridView1.Rows.Count; i++)
            {
                if (this.dataGridView1.Rows[i].Cells[e.ColumnIndex].Value.ToString().Equals(e.Value.ToString()))
                {
                    DownRows++;
                }
                else
                {
                    break;
                }
            }
            //获取上面的行数
            for (int i = e.RowIndex; i >= 0; i--)
            {
                if (this.dataGridView1.Rows[i].Cells[e.ColumnIndex].Value.ToString().Equals(e.Value.ToString()))
                {
                    UpRows++;
                }
                else
                {
                    break;
                }
            }
            count = UpRows + DownRows - 1;//总行数
            using (Brush gridBrush = new SolidBrush(this.dataGridView1.GridColor), backColorBrush = new SolidBrush(e.CellStyle.BackColor))
            {
                using (Pen gridLinePen = new Pen(gridBrush))
                {
                    //清除单元格
                    e.Graphics.FillRectangle(backColorBrush, e.CellBounds);
                    if (e.Value != null)
                    {
                        int cellheight = e.CellBounds.Height;
                        SizeF size = e.Graphics.MeasureString(e.Value.ToString(), e.CellStyle.Font);
                        e.Graphics.DrawString((e.Value).ToString(), e.CellStyle.Font, Brushes.Black, e.CellBounds.X + (cellwidth - size.Width) / 2, e.CellBounds.Y - cellheight * (UpRows - 1) + (cellheight * count - size.Height) / 2, StringFormat.GenericDefault);
                    }
                    //如果下一行数据不等于当前行数据，则画当前单元格底边线
                    if (e.RowIndex < this.dataGridView1.Rows.Count - 1 && this.dataGridView1.Rows[e.RowIndex + 1].Cells[e.ColumnIndex].Value.ToString() != e.Value.ToString())
                    {
                        e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left, e.CellBounds.Bottom - 1, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1);
                    }
                    if (e.RowIndex == this.dataGridView1.Rows.Count - 1)
                    {
                        e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left + 2, e.CellBounds.Bottom - 1, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1);
                        count = 0;
                    }
                    //画grid右边线
                    e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - 1, e.CellBounds.Top, e.CellBounds.Right - 1, e.CellBounds.Bottom);
                    e.Handled = true;
                }
            }
            #endregion
        }
    }