class StackViewController: UIViewController {
	
	let stackView: UIStackView = {
		let v = UIStackView()
		v.axis = .vertical
		return v
	}()
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		// two views to add to the stack view
		let v1 = UIView()
		let v2 = UIView()
		
		// a "container" for the stack view
		let stackContainer = UIView()
		
		v1.backgroundColor = .red
		v2.backgroundColor = .green
		stackContainer.backgroundColor = .yellow
		
		stackView.translatesAutoresizingMaskIntoConstraints = false
		stackContainer.translatesAutoresizingMaskIntoConstraints = false
		
		stackView.addArrangedSubview(v1)
		stackView.addArrangedSubview(v2)
		
		stackContainer.addSubview(stackView)
		view.addSubview(stackContainer)
		
		let g = view.safeAreaLayoutGuide
		
		NSLayoutConstraint.activate([

			// stack view "container" view Top: 40 / centerX
			stackContainer.topAnchor.constraint(equalTo: g.topAnchor, constant: 40.0),
			stackContainer.centerXAnchor.constraint(equalTo: g.centerXAnchor),
			
			// stackView all 4 sides to "container" view
			stackView.topAnchor.constraint(equalTo: stackContainer.topAnchor),
			stackView.leadingAnchor.constraint(equalTo: stackContainer.leadingAnchor),
			stackView.trailingAnchor.constraint(equalTo: stackContainer.trailingAnchor),
			stackView.bottomAnchor.constraint(equalTo: stackContainer.bottomAnchor),
			
			// both arranged subviews 240x160
			v1.widthAnchor.constraint(equalToConstant: 240.0),
			v1.heightAnchor.constraint(equalToConstant: 160.0),
			
			v2.widthAnchor.constraint(equalTo: v1.widthAnchor),
			v2.heightAnchor.constraint(equalTo: v1.heightAnchor),
			
		])
		
		let t = UITapGestureRecognizer(target: self, action: #selector(gotTap(_:)))
		view.addGestureRecognizer(t)
		
	}
	
	@objc func gotTap(_ sender: Any?) -> Void {
		
		// get a reference to the 2nd arranged subview
		guard let v = stackView.arrangedSubviews.last else {
			return
		}
		
		// hide / show
		v.isHidden.toggle()
		
	}
	
}