AnimatingView.swift

private lazy var animatingView: UIView = {
    let view = GradientView(frame: .zero)
    view.gradientLayer.colors = (1...3).map({ "Gradient\($0)" }).map({ UIColor(named: $0)!.cgColor })
    view.translatesAutoresizingMaskIntoConstraints = false
    return view
}()

override func viewDidLoad() {
    super.viewDidLoad()
    view.backgroundColor = .darkGray
    view.addGestureRecognizer(gestureRecognizer)
    view.addSubview(animatingView)
    NSLayoutConstraint.activate([
        animatingView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 72),
        animatingView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -72),
        animatingView.topAnchor.constraint(equalTo: view.topAnchor, constant: 72),
        animatingView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -72)
        ])
}