class ParentViewController: UIViewController {
    @IBAction func redButtonAction(_ sender: Any) {
        PickedColorEvent(color: UIColor.red, name: "RED").fire()
    }
    @IBAction func greenButtonAction(_ sender: Any) {
        PickedColorEvent(color: UIColor.green, name: "GREEN").fire()
    }
    @IBAction func blueButtonAction(_ sender: Any) {
        PickedColorEvent(color: UIColor.blue, name: "BLUE").fire()
    }
    @IBAction func resetButtonAction(_ sender: Any) {
        ResetEvent().fire()
    }
}

class ChildViewController: UIViewController {
    @IBOutlet weak var colorName: UILabel!
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        flow_start()
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        flow_stop()
        super.viewDidDisappear(animated)
    }
}

extension ChildViewController: FlowDispatcher {
    func flow_dispatch(_ event: FlowEvent) {
        if let e = event as? PickedColorEvent {
            view.backgroundColor = e.color
            colorName.text = e.name
        }
        if event is ResetEvent {
            view.backgroundColor = nil
            colorName.text = ""
        }
    }
}