boilerplate code for view controllers root view

CustomView.swift

// boilerplate for uiview subclass that is intended to be used as uiviewcontrollers
// root view using constraints.
class CustomView: UIView {
    // custom views should override this to return true if
    // they cannot layout correctly using autoresizing.
    // from apple docs https://developer.apple.com/documentation/uikit/uiview/1622549-requiresconstraintbasedlayout
    override class var requiresConstraintBasedLayout: Bool {
        return true
    }

    lazy var subView: UIView = {
        // Snazy way of instantiating subviews
        let subView = UIView()
        subView.backgroundColor = .green
        subView.translatesAutoresizingMaskIntoConstraints = false
        return subView
    }()
  
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupView()
    }
  
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupView()
    }
  
    private func setupView() {
        // Configure self
        backgroundColor = .white
        // Add subviews
        addSubview(subView)
        // Configure layout
        setupLayout()
        // setup internal actions for the view
        setupActions()
    }
    
    private func setupActions() {
        // setup the internal actions for the view.
        // addButton.addTarget(self, action: #selector(moveHeaderView), for: .touchUpInside)
    }
    
    private func setupLayout() {
        NSLayoutConstraint.activate([
            subView.topAnchor.constraint(equalTo: topAnchor),
            subView.leadingAnchor.constraint(equalTo: leadingAnchor),
            subView.trailingAnchor.constraint(equalTo: trailingAnchor),
            subView.heightAnchor.constraint(equalToConstant: 40)
        ])
    }
}