override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let button = UIButton(type: .system)
        button.setTitle("ahoj", for: .normal)
        view.addSubview(button)
        button.translatesAutoresizingMaskIntoConstraints = false
        button.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        button.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true

        button.addAction(for: .touchUpInside) {
            print("ahoj")
        }
    }