C2ViewController.swift

class C2ViewController: UIViewController {
	
	var myCustomAlertView = CustomAlertView()

	override func viewDidLoad() {
		super.viewDidLoad()
		
		if var topController = UIApplication.shared.delegate?.window??.rootViewController {
			while let presentedViewController = topController.presentedViewController {
				topController = presentedViewController
			}

			myCustomAlertView = CustomAlertView("Here is a message - Hello!")
			myCustomAlertView.translatesAutoresizingMaskIntoConstraints = false
			
			topController.view.addSubview(myCustomAlertView)
			
			myCustomAlertView.topAnchor.constraint(equalTo: topController.view.topAnchor, constant: 0.0).isActive = true
			myCustomAlertView.bottomAnchor.constraint(equalTo: topController.view.bottomAnchor, constant: 0.0).isActive = true
			myCustomAlertView.leadingAnchor.constraint(equalTo: topController.view.leadingAnchor, constant: 0.0).isActive = true
			myCustomAlertView.trailingAnchor.constraint(equalTo: topController.view.trailingAnchor, constant: 0.0).isActive = true
			
		}
		
	}
	
}

class CustomAlertView: UIView {
	
	lazy var theLabel: UILabel = {
		let v = UILabel()
		v.backgroundColor = .yellow
		v.textAlignment = .center
		v.numberOfLines = 0
		v.translatesAutoresizingMaskIntoConstraints = false
		return v
	}()
	
	convenience init(_ withString: String) {
		self.init(frame: CGRect.zero)
		theLabel.text = "The passed string is:\n\n\(withString)"
	}
	
	override init(frame: CGRect) {
		super.init(frame: frame)
		
		backgroundColor = .black
		alpha = 0.60
		
		addSubview(theLabel)
		
		theLabel.centerXAnchor.constraint(equalTo: centerXAnchor, constant: 0.0).isActive = true
		theLabel.centerYAnchor.constraint(equalTo: centerYAnchor, constant: 0.0).isActive = true

	}
	
	required init?(coder aDecoder: NSCoder) {
		fatalError("init(coder:) has not been implemented")
	}
	
}