Iphone 如何为单个uitableview单元格提供圆形边框

我有一个UIviewController，在xib文件中我添加了3个uitableview单元格，但我想给顶部和底部单元格提供圆角，类似于分组表格的外观。如何做到这一点，以及如何以编程方式将表格单元格添加到uiviewcontroller？

以下是我的方法，但要实现这一点，您需要为顶部单元格、底部单元格和中间单元格创建一个图像。这将有助于区分第一行、中间行和底部行

    UIImage *rowBackground;
    UIImage *selectionBackground;
    NSInteger sectionRows = [tableView numberOfRowsInSection:[indexPath section]];
    if (indexPath.row == 0)
    {
        rowBackground = [UIImage imageNamed:@"topRow.png"]; //Top Rounded
        selectionBackground = [UIImage imageNamed:@"topRowSelected.png"]; //Top Rounded Selected
    }
    else if (indexPath.row == sectionRows - 1)
    {
        if (indexPath.section == 0) {
        rowBackground = [UIImage imageNamed:@"bottomRow.png"];// Bottom Rounded
        selectionBackground = [UIImage imageNamed:@"bottomRowSelected.png"]; //Bottom Rounded Selected
        } else {
            rowBackground = [UIImage imageNamed:@"bottomRowSelected.png"];
            selectionBackground = [UIImage imageNamed:@"bottomRow.png"];
        }
    }
    else
    {
        rowBackground = [UIImage imageNamed:@"middleRow.png"]; // Anything in the middle
        selectionBackground = [UIImage imageNamed:@"middleRowSelected.png"];
    }

    ((UIImageView *)cell.backgroundView).image = rowBackground;
    ((UIImageView *)cell.selectedBackgroundView).image = selectionBackground;