oc的方法

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
    // 圆角角度
    CGFloat radius = 10.f;
    // 设置cell 背景色为透明
    cell.backgroundColor = UIColor.clearColor;
    // 创建两个layer
    CAShapeLayer *normalLayer = [[CAShapeLayer alloc] init];
    CAShapeLayer *selectLayer = [[CAShapeLayer alloc] init];
    // 获取显示区域大小
    CGRect bounds = CGRectInset(cell.bounds, kScaleX * 20, 0);
    // cell的backgroundView
    UIView *normalBgView = [[UIView alloc] initWithFrame:bounds];
    // 获取每组行数
    NSInteger rowNum = [tableView numberOfRowsInSection:indexPath.section];
    // 贝塞尔曲线
    UIBezierPath *bezierPath = nil;
    
    if (rowNum == 1) {
        // 一组只有一行（四个角全部为圆角）
        bezierPath = [UIBezierPath bezierPathWithRoundedRect:bounds byRoundingCorners:UIRectCornerAllCorners cornerRadii:CGSizeMake(radius, radius)];
        normalBgView.clipsToBounds = NO;
    }else {
        normalBgView.clipsToBounds = YES;
        if (indexPath.row == 0) {
            normalBgView.frame = UIEdgeInsetsInsetRect(bounds, UIEdgeInsetsMake(-5, 0, 0, 0));
            CGRect rect = UIEdgeInsetsInsetRect(bounds, UIEdgeInsetsMake(5, 0, 0, 0));
            // 每组第一行（添加左上和右上的圆角）
            bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:(UIRectCornerTopLeft|UIRectCornerTopRight) cornerRadii:CGSizeMake(radius, radius)];
        }else if (indexPath.row == rowNum - 1) {
            normalBgView.frame = UIEdgeInsetsInsetRect(bounds, UIEdgeInsetsMake(0, 0, -5, 0));
            CGRect rect = UIEdgeInsetsInsetRect(bounds, UIEdgeInsetsMake(0, 0, 5, 0));
            // 每组最后一行（添加左下和右下的圆角）
            bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:(UIRectCornerBottomLeft|UIRectCornerBottomRight) cornerRadii:CGSizeMake(radius, radius)];
        }else {
            // 每组不是首位的行不设置圆角
            bezierPath = [UIBezierPath bezierPathWithRect:bounds];
        }
    }
    
    // 阴影
    normalLayer.shadowColor = [UIColor blackColor].CGColor;
    normalLayer.shadowOpacity = 0.2;
    normalLayer.shadowOffset = CGSizeMake(0, 0);
    normalLayer.path = bezierPath.CGPath;
    normalLayer.shadowPath = bezierPath.CGPath;
    
    // 把已经绘制好的贝塞尔曲线路径赋值给图层，然后图层根据path进行图像渲染render
    normalLayer.path = bezierPath.CGPath;
    selectLayer.path = bezierPath.CGPath;
    
    // 设置填充颜色
    normalLayer.fillColor = [UIColor whiteColor].CGColor;
    // 添加图层到nomarBgView中
    [normalBgView.layer insertSublayer:normalLayer atIndex:0];
    normalBgView.backgroundColor = UIColor.clearColor;
    cell.backgroundView = normalBgView;
    
    // 替换cell点击效果
    UIView *selectBgView = [[UIView alloc] initWithFrame:bounds];
    selectLayer.fillColor = [UIColor colorWithWhite:0.95 alpha:1.0].CGColor;
    [selectBgView.layer insertSublayer:selectLayer atIndex:0];
    selectBgView.backgroundColor = UIColor.clearColor;
    cell.selectedBackgroundView = selectBgView;
}

swift

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        // 圆角角度
        let radius = 10.zoom()
        
        // 设置cell 背景色为透明
        cell.backgroundColor = .clear
        
        // 创建两个layer
        let normalLayer = CAShapeLayer()
        let selectLayer = CAShapeLayer()
        
        // 获取显示区域大小
        let bounds = cell.bounds.insetBy(dx: 15.zoom(), dy: 0)
        
        // cell的backgroundView
        let normalBgView = UIView(frame: bounds)
        
        // 获取每组行数
        let rowNum = tableview.numberOfRows(inSection: indexPath.section)
        var bezierPath:UIBezierPath
        
        normalBgView.clipsToBounds = true
        if indexPath.row == 0 {
//           每组第一行
            normalBgView.frame = bounds.inset(by: UIEdgeInsets(top: -5.zoom(), left: 0, bottom: 0, right: 0))
            let rect = bounds.inset(by: UIEdgeInsets(top: 5.zoom(), left: 0, bottom: 0, right: 0))
            
            // 每组第一行（添加左上和右上的圆角）
            bezierPath = UIBezierPath(roundedRect: rect, byRoundingCorners: [.topLeft,.topRight], cornerRadii: CGSize(width: radius, height: radius))
        }else if indexPath.row == rowNum - 1 {
//            每组最后一行
            normalBgView.frame = bounds.inset(by: UIEdgeInsets(top: 0, left: 0, bottom: -2.zoom(), right: 0))
            let rect = bounds.inset(by: UIEdgeInsets(top: 0, left: 0, bottom: 2.zoom(), right: 0))
            
            // 每组最后一行（添加左下和右下的圆角）
            bezierPath = UIBezierPath(roundedRect: rect, byRoundingCorners: [.bottomLeft,.bottomRight], cornerRadii: CGSize(width: radius, height: radius))
        }else{
            
            // 每组不是首位的行不设置圆角
            bezierPath = UIBezierPath(rect: bounds)
        }
        
        // 阴影
        normalLayer.shadowColor = UIColor.black.cgColor
        normalLayer.shadowOpacity = 0.2
        normalLayer.shadowOffset = CGSize(width: 0, height: 0)
        normalLayer.path = bezierPath.cgPath
        normalLayer.shadowPath = bezierPath.cgPath
        
        // 把已经绘制好的贝塞尔曲线路径赋值给图层，然后图层根据path进行图像渲染render
        normalLayer.path = bezierPath.cgPath
        selectLayer.path = bezierPath.cgPath
        
        // 设置填充颜色
        normalLayer.fillColor = UIColor.white.cgColor
        
        // 添加图层到nomarBgView中
        normalBgView.layer .insertSublayer(normalLayer, at: 0)
        normalBgView.backgroundColor = UIColor.clear
        cell.backgroundView = normalBgView
        
        // 替换cell点击效果
        let selectBgView = UIView(frame: bounds)
        selectLayer.fillColor = UIColor.init(white: 0.95, alpha: 1).cgColor
        selectBgView.layer .insertSublayer(selectLayer, at: 0)
        selectBgView.backgroundColor = UIColor.clear
        cell.selectedBackgroundView = selectBgView
        
    }