Winform中DataGridView下拉框单元格错误时，改变背景色，作为提示

在错误的条件时，更改cell.Style.BackColor的背景颜色

 /// <summary>
 /// 单元格字体颜色
 /// </summary>
 Color cellForeColor = Color.Black;
 /// <summary>
 /// 单元格背景正常颜色
 /// </summary>
 Color cellNomalColor = Color.White;
 /// <summary>
 /// 单元格背景错误颜色
 /// </summary>
 Color cellErrorColor = Color.Red;
 /// <summary>
 /// 编辑单元格
 /// </summary>
 private void dgvGroupConfig_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
 {
     isDrawToString = false;
     if (e.Control is DataGridViewComboBoxEditingControl cb)
     {
         cb.DropDownStyle = ComboBoxStyle.DropDownList;
         cb.DrawMode = DrawMode.OwnerDrawFixed;
         cb.DrawItem -= Cb_DrawItem;
         cb.DrawItem += Cb_DrawItem;
     }
     var dgv = sender as DataGridView;
     if (dgv.CurrentCell.ColumnIndex == cbxDriller.Index
         || dgv.CurrentCell.ColumnIndex == cbxSupervisor.Index)
     {
         isDrawToString = true;
     }
 }
 bool isDrawToString = false;
 /// <summary>
 /// 单元格重绘
 /// </summary>
 /// <param name="sender"></param>
 /// <param name="e"></param>
 private void Cb_DrawItem(object sender, DrawItemEventArgs e)
 {
     if (e.Index < 0)
     {
         return;
     }

     if (sender is DataGridViewComboBoxEditingControl cb)
     {
         cb.BackColor = cellNomalColor;
         string value = cb.GetItemText(cb.Items[e.Index]);
         if (isDrawToString)
             value = cb.Items[e.Index].ToString();
         using (Brush foreBrush = new SolidBrush(cellForeColor))
         using (Brush backBrush = new SolidBrush(cb.BackColor))
         {
             e.Graphics.FillRectangle(backBrush, e.Bounds);
             e.DrawBackground();
             e.DrawFocusRectangle();
             e.Graphics.DrawString(value, cb.Font, foreBrush, e.Bounds);
         }
     }
 }

 /// <summary>
 /// 重新编写单元格绘制函数
 /// </summary>
 private void dgvGroupConfig_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
 {
     var dgv = sender as DataGridView;
     if (e.ColumnIndex < 0 || e.RowIndex < 0)
     {
         return;
     }
     if (dgv.Rows[e.RowIndex].Cells[e.ColumnIndex] is DataGridViewComboBoxCell cell)
     {
         e.Paint(e.ClipBounds, DataGridViewPaintParts.Border);
         e.Paint(e.ClipBounds, DataGridViewPaintParts.ContentBackground);

         using (Brush foreBrush = new SolidBrush(cellForeColor))
         using (Brush backBrush = new SolidBrush(cell.Style.BackColor))
         using (StringFormat format = new StringFormat())
         {
             Rectangle rect = new Rectangle(e.CellBounds.X + 1, e.CellBounds.Y + 1, e.CellBounds.Width - 19, e.CellBounds.Height - 3);
             format.LineAlignment = StringAlignment.Center;
             e.Graphics.FillRectangle(backBrush, rect);
             e.Graphics.DrawString(cell.FormattedValue.ToString(), e.CellStyle.Font, foreBrush, rect, format);
         }

         e.Paint(e.ClipBounds, DataGridViewPaintParts.ErrorIcon);
         e.Paint(e.ClipBounds, DataGridViewPaintParts.Focus);
         e.Handled = true;
     }
 }