datagridview合并相同单元格

private void dataGridView1_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
        {
            // 对第日期列相同单元格进行合并
            if (e.ColumnIndex ==  && e.RowIndex != -)
            {
                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);

                            // 画 Grid 边线（仅画单元格的底边线和右边线）
                            // 如果下一行和当前行的数据不同，则在当前的单元格画一条底边线
                            if (e.RowIndex < dataGridView1.Rows.Count -  &&
                            dataGridView1.Rows[e.RowIndex + ].Cells[e.ColumnIndex].Value.ToString() != e.Value.ToString())
                            {
                                e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left,
                                e.CellBounds.Bottom - , e.CellBounds.Right - ,
                                e.CellBounds.Bottom - );

                            }
                            //如果是最后一行，画上底线避免一个缺口
                            if (e.RowIndex == dataGridView1.Rows.Count - )
                            {
                                e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left,
                                e.CellBounds.Bottom - , e.CellBounds.Right - ,
                                e.CellBounds.Bottom - );
                            }
                            // 画右边线
                            e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - ,
                                e.CellBounds.Top, e.CellBounds.Right - ,
                                e.CellBounds.Bottom);

                            // 画（填写）单元格内容，相同的内容的单元格只填写第一个
                            if (e.Value != null)
                            {
                                if (e.RowIndex >  && dataGridView1.Rows[e.RowIndex - ].Cells[e.ColumnIndex].Value.ToString() == e.Value.ToString())
                                {
                                }
                                else
                                {
                                    e.Graphics.DrawString((String)e.Value, e.CellStyle.Font,
                                    Brushes.Black, e.CellBounds.X + ,
                                    e.CellBounds.Y + , StringFormat.GenericDefault);
                                }
                            }
                            e.Handled = true;
                        }
                }
            }
        }