UITableView cell加圆角

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        let radius = 8.0 //圆角
        cell.backgroundColor = .clear
        let normalLayer = CAShapeLayer()
        let selectLayer = CAShapeLayer()
        let bounds = cell.bounds.insetBy(dx:10.0, dy:0) //cell 左右缩进距离
        let rowNum = tableView.numberOfRows(inSection: indexPath.section)
        var bezierPath:UIBezierPath
        if(rowNum==1) {
            bezierPath = UIBezierPath(roundedRect: bounds, byRoundingCorners: .allCorners, cornerRadii:CGSize(width: radius, height: radius))
        }else{
            if(indexPath.row==0) {
                bezierPath = UIBezierPath(roundedRect: bounds, byRoundingCorners:[UIRectCorner.topLeft,UIRectCorner.topRight], cornerRadii:CGSize(width: radius, height: radius))
            }else if(indexPath.row==rowNum-1) {
                bezierPath = UIBezierPath(roundedRect: bounds, byRoundingCorners: [UIRectCorner.bottomLeft,UIRectCorner.bottomRight], cornerRadii:CGSize(width: radius, height: radius))
            }else{
                bezierPath = UIBezierPath(rect: bounds)
            }
        }
        normalLayer.path = bezierPath.cgPath
        selectLayer.path = bezierPath.cgPath
        let nomarBgView = UIView(frame: bounds)
        normalLayer.fillColor = UIColor(51, 51, 64).cgColor
        nomarBgView.layer.insertSublayer(normalLayer, at:0)
        nomarBgView.backgroundColor = .clear
        cell.backgroundView = nomarBgView
        let selectBgView = UIView(frame: bounds)
        selectLayer.fillColor = UIColor(213.0, 230.0, 244.0).cgColor
        selectBgView.layer.insertSublayer(selectLayer, at:0)
        cell.selectedBackgroundView = selectBgView
    }