setViewControllers doesn't work

Question

I'm trying to change the current ViewController of my UIPageViewController using a NEXT button. So I'm calling the function that's in my containterViewController in my mainViewController using a delegate. But it doesn't execute the setViewControllers line.

Here you can see my code:

This is the method that I call using my delegate:

func forwardPage() {
    print("Start")
    currentPage += 1
    print(vcs[currentPage])
    self.setViewControllers([vcs[currentPage]], direction: .forward, animated: true) { (true) in
        print("Done")
    }
}

Here's my delegate:

protocol WalkthroughViewControllerDelegate {
   func forwardPage()
   func currentIndex() -> Int
}

And here's the function that is connected to my NEXT button:

@IBAction func nextButtonTapped(_ sender: Any) {
    if let index = delegate?.currentIndex() {
        print("Here... \(index)")
        switch index {
        case 0...1:
            print("Forwarding...")
            delegate?.forwardPage()
        case 2:
            dismiss(animated: true, completion: nil)
        default: break
        }
    }

    updateUI()
}

Everything but the "Done" gets printed

I would really appreciate your help

I've been struggling because of this for quite some time now

Thank you very much :)

EDIT: Maybe this happens because that UIPageViewController is inside a containerView. But I'm not sure

SECOND EDIT: I've created a git-hub repository just for this issue. Here's the link: https://github.com/LennartPhil/App-Popup-Screen. I hope you can understand that I won't show you all of my files.

Answer 1

OK - the problem is that your code in viewDidLoad():

    let storyboard = UIStoryboard(name: "ExtraViewControllers", bundle: nil)
    let walkthroughPageVC = storyboard.instantiateViewController(withIdentifier: "WalkthroughPageVC") as! WalkthroughPageViewController
    delegate = walkthroughPageVC

is creating a NEW instance of WalkthroughPageViewController, which goes out of scope as soon as viewDidLoad() exits. So it no longer exists.

What you need to do instead is get a reference to it in prepare(for segue:...), and set it as your delegate there:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if let vc = segue.destination as? WalkthroughPageViewController {
        self.delegate = vc
    }
}

I forked your GitHub repo and added the files into a project, so you can see it run: https://github.com/DonMag/App-Popup-Screen