UIViewController+Extension.swift

extension UIViewController {
    private class ExtendedBottomView: UIView { }
    
    /// Create bottom View which covers from bottom of the screen to the
    /// bottom edge of the bottomAccessoryView.
    /// (useful on iPhone X only)
    /// Make sure not to call more than once (typically, on viewDidLoad),
    /// and bottomAccessoryView has added as subview.
    ///
    /// - parameter bottomAccessoryView: a target View to decide the
    /// top-edge of bottomView
    func addBottomView(to bottomAccessoryView: UIView) {
        guard let bottomSuperView = bottomAccessoryView.superview,
            let view = view,
            bottomSuperView == view else {
                return
        }
        guard !view.subviews.contains(where: { $0 is ExtendedBottomView }) else {
            assertionFailure("View cannot be added more than once")
            return
        }
        let bottomView = ExtendedBottomView()
        view.addSubview(bottomView)
        bottomView.translatesAutoresizingMaskIntoConstraints = false
        bottomView.backgroundColor = bottomAccessoryView.backgroundColor
        NSLayoutConstraint.activate([
            bottomView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            bottomView.leftAnchor.constraint(equalTo: view.leftAnchor),
            bottomView.rightAnchor.constraint(equalTo: view.rightAnchor),
            bottomView.topAnchor.constraint(equalTo: bottomAccessoryView.bottomAnchor)
            ])
        bottomView.setNeedsLayout()
    }
}