How to check when UIPageViewController VC changes to another?

Question

I try to check when my UIPageViewController's VC changes to another by swiping. What function handles this, and how I can get the new page index?

I know about function:

func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
  //code
}

Thanks very much.

Answer 1

This little bit of code should do the trick:

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {

    guard completed else { return }

    guard let index = (pageViewController.viewControllers?.first as? ContentViewController)?.index else { return }

    guard let index = pageViewController.viewControllers?.first?.view.tag else { return }

    guard let vc = pageViewController.viewControllers?.first else { return }

    let index: Int

    switch vc {
    case is FirstViewController:
        index = 0
    case is SecondViewController:
        index = 1
    default:
        index = 2
    }
}

What you do here is manually saving the currently selected index. This should work as long as the transition is animated, which it should always be I guess.