Swift：给UITableView的section添加阴影

话不多少，上代码：

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        // 在该方法下对每个section设置阴影
        // 圆角角度
        let radius = kMarginMid
        // 设置cell 背景色为透明
        cell.backgroundColor = .clear
        // 创建layer
        let normalLayer = CAShapeLayer()
        // 获取显示区域大小
        let bounds = cell.bounds.insetBy(dx: kMarginMid, dy: 0)
        // cell的backgroundView
        let normalBgView = UIView(frame: bounds)
        // 获取每组行数
        let rowNum = tableView.numberOfRows(inSection: indexPath.section)
        // 贝塞尔曲线
        var bezierPath = UIBezierPath()
        if rowNum == 1 {
            // 一组只有一行（四个角全部为圆角）
            bezierPath = UIBezierPath(roundedRect: bounds, byRoundingCorners: .allCorners, cornerRadii: CGSize(width: radius, height: radius))
            normalBgView.clipsToBounds = false
        } else {
            normalBgView.clipsToBounds = true
            if indexPath.row == 0 {
                let top = indexPath.section == 0 ? kMarginMin : RW(5)
                let rect = bounds.inset(by: UIEdgeInsets(top: top, 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 {
                let rect = bounds.inset(by: UIEdgeInsets(top: 0, left: 0, bottom: RW(5), 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 = 0.15
        normalLayer.shadowOffset  = CGSize(width: 0, height: 1)
        normalLayer.path          = bezierPath.cgPath
        normalLayer.shadowPath    = bezierPath.cgPath
        // 设置填充颜色
        normalLayer.fillColor        = UIColor.white.cgColor
        // 添加图层到nomarBgView中
        normalBgView.backgroundColor = UIColor.clear
        // 如果是第一个分区,那么需要再额外加一层
        if indexPath.section == 0 && indexPath.row == 0 {
            normalBgView.backgroundColor = APP_MainColor
            let basicLayer  = CAShapeLayer()
            basicLayer.path = UIBezierPath(roundedRect: cell.bounds, byRoundingCorners: [.topLeft, .topRight], cornerRadii: CGSize(width: RW(22.5), height: RW(22.5))).cgPath
            basicLayer.fillColor = UIColor.white.cgColor
//            normalBgView.layer.insertSublayer(basicLayer, at: 0)
            basicLayer.addSublayer(normalLayer)
            normalBgView.layer.insertSublayer(basicLayer, at: 0)
        } else {
            normalBgView.layer.insertSublayer(normalLayer, at: 0)
        }
        cell.backgroundView          = normalBgView
    }