dataGridView通过重绘合并单元格的问题

Question

  private void dataGridView1_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
         {
            // 对第1列相同单元格进行合并
            if (e.ColumnIndex == 0 && e.RowIndex != -1)
             {
                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 - 1 &&
                         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);
                        // 画右边线
                         e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - 1,
                             e.CellBounds.Top, e.CellBounds.Right - 1,
                             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 > 0 &&
                             dataGridView1.Rows[e.RowIndex - 1].Cells[e.ColumnIndex].Value.ToString() == 
                             e.Value.ToString())
                             { }
                            else
                             {
                                 e.Graphics.DrawString((String)e.Value, e.CellStyle.Font,
                                     Brushes.Black, e.CellBounds.X + 2,
                                     e.CellBounds.Y + 5, StringFormat.GenericDefault);
                             }
                         }
                         e.Handled = true;
                     }
                 }
             }帮忙看看上面的代码,编译在这句//    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 - 1 &&
                         dataGridView1.Rows[e.RowIndex + 1].Cells[e.ColumnIndex].Value.ToString() != 
                         e.Value.ToString())提示出错,逻辑上 没什么问题啊,提示有个对象为实例化,我猜测毛病处在最后一个单元格的绘制上,但是我找不出毛病在哪里,请大家帮忙看看.

Answer 1

那是因为最后一行是空,所以得加多一个判断是否为null:
 if (e.RowIndex < dataGridView1.Rows.Count - 1 &&
 dataGridView1.Rows[e.RowIndex + 1].Cells[e.ColumnIndex].Value!=null &&
e.Value!=null &&
                        dataGridView1.Rows[e.RowIndex + 1].Cells[e.ColumnIndex].Value.ToString() != 
                        e.Value.ToString())