在带有曲线的选项卡上方添加顶线

Question

有没有办法设置仅在Tabbar顶部具有曲线边缘的线？

喜欢这张图片

我尝试了以下代码：

//Add top white line above tabbar
    let lineView = UIView(frame: CGRect(x: 0, y: 0, width:self.tabBar.frame.size.width, height: 3))
    lineView.backgroundColor = UIColor.white
    lineView.layer.masksToBounds = true
    lineView.clipsToBounds = true
    lineView.layer.cornerRadius = 20.0
    self.tabBar.layer.borderColor = UIColor.green.cgColor
    self.tabBar.layer.borderWidth = 3
    self.tabBar.addSubview(lineView)

但是它将图层添加到整个Tabbar。

我也尝试过此代码：

     // Add rounded corners
    let maskLayer = CAShapeLayer()
    maskLayer.frame = self.tabBar.bounds
    maskLayer.path = UIBezierPath(roundedRect: self.tabBar.bounds, byRoundingCorners: [.topLeft, .topRight], cornerRadii: CGSize(width: 20, height: 20)).cgPath
    self.tabBar.layer.mask = maskLayer

    // Add border
    let borderLayer = CAShapeLayer()
    borderLayer.path = maskLayer.path
    borderLayer.fillColor = UIColor.clear.cgColor

    borderLayer.strokeColor = UIColor.green.cgColor
    borderLayer.lineWidth = 3
    borderLayer.frame = self.tabBar.bounds
    self.tabBar.layer.addSublayer(borderLayer)

但是问题是相同的，它正在添加到整个视图中