设置阴影时，又去设置 masksToBounds = true 阴影效果就不会显示。
let shadowView = UIView(frame: CGRect(x: 100, y: 100, width: 100, height: 100))
shadowView.backgroundColor = .yellow
shadowView.layer.shadowColor = UIColor.black.cgColor
shadowView.layer.shadowOffset = CGSize(width: 5, height: 5)
shadowView.layer.shadowOpacity = 1
shadowView.layer.shadowRadius = 10
shadowView.layer.cornerRadius = 5
// 设置阴影 又同时设置 masksToBounds 会被裁剪掉，效果不显示
// shadowView.layer.masksToBounds = true
view.addSubview(shadowView)
