Reliable way to track Page Index in a UIPageViewController - Swift

Question

I have a UIPageViewController (custom one) inside a Container located in a regular UIViewController. i need to be able to call an event with each Page Change but ONLY if it really did change and not only half way or anything of that sort.

using:

func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController?

is unreliable and not called each time for some reason.

if your answer contains anything about willTransitionToViewControllers or didFinishAnimating please elaborate and not just mention them, since i already know they exist but dont understand the proper way to use them.

Thank you

James P · Accepted Answer · 2016-07-27T15:09:44.923

5

Use didFinishAnimating it has a completed and finished property so you know the page has actually changed. From the pageViewController you can get the currently displayed page, then get the position of this VC in your model.

First make sure your ViewController adopts UIPageViewControllerDelegate

Set the delegate (e.g. in viewDidLoad)

pageViewController.delegate = self

Then implement the following function:

    func pageViewController(pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        if (completed && finished) {
            if let currentVC = pageViewController.viewControllers?.last {
                let index = myViewControllers.indexOf(currentVC)
                //do something with index
            }
        }
    }

edited Jul 27 '16 at 15:09

answered Jul 27 '16 at 11:07

James P

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Thank you so very much James, it solved my problem :) in case any other beginners find this solution: dont forget to add UIPageViewControllerDelegate at the class declaration to allow this function to be called. – MarkosDarkin Jul 27 '16 at 14:38
No worries, I've added your comment to the answer. – James P Jul 27 '16 at 14:46
appreciate it James :) – MarkosDarkin Jul 27 '16 at 16:14
1

What is the value of "myViewControllers", and how to set it? – Nupur Sharma Nov 20 '17 at 05:48
When would the viewControllers array ever contain more than 1? – Script Kitty May 04 '18 at 16:26
@ScriptKitty One reason would be if the spineLocation is set to `mid`. – James P May 08 '18 at 08:44

Reliable way to track Page Index in a UIPageViewController - Swift

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