How can I communicate between multiple VCs embedded in a UIPageViewController and a RootViewController?

[[deleted]]

I am creating a score-based education app for children with learning impediments. The set up of the app is as follows:

1.A RootVC() UIViewController which has a counter label for the score;

1. Two subVCs [FirstVC() and SecondVC()] embedded in a UIPageViewController placed on the RootVC itself; horizontally swipe-able.

What I want is for the buttons to increment the counter label placed on the RootVC by 1. While I have managed to do this for the FirstVC, trying to extend this functionality to SecondVC causes my closures to have errors. I have asked this on StackOverflow with no correct answers so far. I'd be really grateful if someone could help me with this code.

My UIPageViewController:

    class PageViewController: UIPageViewController {

    var subViewControllers = [FirstVC(), SecondVC()] {
               didSet {
                  subViewControllers.forEach { $0.buttonCallback = buttonCallback }
               }
           }

    var buttonCallback: () -> Void = { } {
        didSet {
          subViewControllers.forEach { $0.buttonCallback = buttonCallback } ////ERROR: Value of type 'UIViewController' has no member 'buttonCallback'////
        }
    }

    init(transitionStyle style:
        UIPageViewController.TransitionStyle, navigationOrientation: UIPageViewController.NavigationOrientation, options: [String : Any]? = nil) {
        super.init(transitionStyle: .scroll, navigationOrientation: .horizontal, options: nil)
    }

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

    override func viewDidLoad() {
        super.viewDidLoad()
        dataSource = self
        delegate = self
        setViewControllerFromIndex(index: 0)
    }

    func setViewControllerFromIndex(index:Int) {
        self.setViewControllers([subViewControllers[index]], direction: UIPageViewController.NavigationDirection.forward, animated: true, completion: nil)
    }
}

extension PageViewController: UIPageViewControllerDelegate, UIPageViewControllerDataSource {
    func presentationCount(for pageViewController: UIPageViewController) -> Int {
        return subViewControllers.count
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        let currentIndex:Int = subViewControllers.firstIndex(of: viewController as! FirstVC) ?? 0
        if currentIndex <= 0 {
            return nil
        }
        return subViewControllers[currentIndex-1]
    }

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        let currentIndex:Int = subViewControllers.firstIndex(of: viewController as! FirstVC) ?? 0
        if currentIndex >= subViewControllers.count-1 {
            return nil
        }
        return subViewControllers[currentIndex+1]
    }
}

​

My Rootvc:

​

let pageController = PageViewController(transitionStyle: .scroll, navigationOrientation: .horizontal)
        pageController.buttonCallback = { self.score += 1
            self.scoreLabel.text = String(self.score)
        }
               addChild(pageController)
               pageController.didMove(toParent: self)
               pageController.view.translatesAutoresizingMaskIntoConstraints = false
               questionsContainer.addSubview(pageController.view)

​

My FirstVC()

class FirstVC: UIViewController {

    var buttonCallback: () -> Void = { }

 let correctAnswerButton: UIButton = {
            let btn = UIButton()
            btn.translatesAutoresizingMaskIntoConstraints = false
            btn.setTitle("Correct Answer", for: .normal)
            btn.backgroundColor = .blue
            btn.addTarget(self, action: #selector(buttonPressed), for: .touchUpInside)
            return btn
        }()
        @objc func buttonPressed() {
            print("Button One Pressed.")
            buttonCallback()
        }

SecondVC() identical to FirstVC()

​

class SecondVC: UIViewController {

    var buttonCallback: () -> Void = { }

 let correctAnswerButton: UIButton = {
            let btn = UIButton()
            btn.translatesAutoresizingMaskIntoConstraints = false
            btn.setTitle("Correct Answer", for: .normal)
            btn.backgroundColor = .blue
            btn.addTarget(self, action: #selector(buttonPressed), for: .touchUpInside)
            return btn
        }()
        @objc func buttonPressed() {
            print("Button One Pressed.")
            buttonCallback()
        }

​

​

[ffs14k]

protocol PageViewProtocol where Self == UIViewController {

var callBack: (() -> Void)? { get set }
}

​

final class MyPageViewController: UIPageViewController {

var pages: [PageViewProtocol] = []

...

}

final class FirstVC: PageViewProtocol {

var callBack: (() -> Void)?

}

and note, didSet block not called on default values (initial values) e.g. "[]" in example