实现这一点的技巧是在中间放置另一个视图，该视图剪辑顶视图的内容。检查以下代码：

let bottomShadowView = UIView(frame: CGRect(x: 100.0, y: 100.0, width: 200.0, height: 100.0))
bottomShadowView.backgroundColor = .white
bottomShadowView.layer.cornerRadius = 20.0
bottomShadowView.layer.shadowColor = UIColor.black.cgColor
bottomShadowView.layer.shadowOpacity = 0.2
bottomShadowView.layer.shadowRadius = 8
view.addSubview(bottomShadowView)

let bottomClipView = UIView(frame: bottomShadowView.bounds)
bottomClipView.layer.cornerRadius = bottomShadowView.layer.cornerRadius
bottomClipView.clipsToBounds = true
bottomShadowView.addSubview(bottomClipView)

let topShadowView = UIView(frame: CGRect(x: 0.0, y: 0.0, width: 200.0, height: 50.0))
topShadowView.backgroundColor = .white
topShadowView.layer.cornerRadius = 20.0
topShadowView.layer.shadowColor = UIColor.black.cgColor
topShadowView.layer.shadowOpacity = 0.2
topShadowView.layer.shadowRadius = 8
bottomClipView.addSubview(topShadowView)

请注意，您可以在接口构建器中完成大部分工作，但代码应该能给予您更好地理解正在发生的事情。
bottomClipView需要与父阴影视图具有相同的大小，并具有相同的特征，例如拐角半径。然后简单地应用clipsToBounds，这样你在这个视图上放置的任何东西都不会画出它的边界，也不会干扰阴影。