Get scroll position of UIPageViewController

Question

I am using a UIPageViewController, and I need to get the scroll position of the ViewController as the users swipe so I can partially fade some assets while the

Answer 1

UIPageViewController scroll doesn't work like normal scrollview and you can't get scrollView.contentOffset like other scrollViews.

so here is a trick to get what's going on when user scrolls :

first you have to find scrollview and set delegate to current viewController like other answers said.

class YourViewController : UIPageViewController {

    var startOffset = CGFloat(0) //define this

    override func viewDidLoad() {
         super.viewDidLoad()

         //from other answers   
         for v in view.subviews{
             if v is UIScrollView {
                 (v as! UIScrollView).delegate = self
             }
         }
     }

    .
    .
    .
}

extension YourViewController : UIScrollViewDelegate{

    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {

        startOffset = scrollView.contentOffset.x
    }

    public func scrollViewDidScroll(_ scrollView: UIScrollView) {

        var direction = 0 //scroll stopped

        if startOffset < scrollView.contentOffset.x {
            direction = 1 //going right
        }else if startOffset > scrollView.contentOffset.x {
            direction = -1 //going left
        }

        let positionFromStartOfCurrentPage = abs(startOffset - scrollView.contentOffset.x)
        let percent = positionFromStartOfCurrentPage /  self.view.frame.width

        //you can decide what to do with scroll
    }

}

Answer 2

Similar to Christian's answer but a bit more Swift-like (and not unnecessarily continuing to loop through view.subviews):

for view in self.view.subviews {
    if let view = view as? UIScrollView {
        view.delegate = self
        break
    }
}

Answer 3

You can search for the UIScrollView inside your UIPageViewController. To do that, you will have to implement the UIScrollViewDelegate.

After that you can get your scrollView:

for v in pageViewController.view.subviews{
    if v.isKindOfClass(UIScrollView){
        (v as UIScrollView).delegate = self
    }
}

After that, you are able to use all the UIScrollViewDelegate-methods and so you can override the scrollViewDidScroll method where you can get the scrollPosition:

func scrollViewDidScroll(scrollView: UIScrollView) {
   //your Code
}

---

Or if you want a one-liner:

let scrollView = view.subviews.filter { $0 is UIScrollView }.first as! UIScrollView
scrollView.delegate = self

Answer 4

var pageViewController: PageViewController? {
    didSet {
        pageViewController?.dataSource = self
        pageViewController?.delegate = self
        scrollView?.delegate = self
    }
}

lazy var scrollView: UIScrollView? = {
    for subview in pageViewController?.view?.subviews ?? [] {
        if let scrollView = subview as? UIScrollView {
            return scrollView
        }
    }
    return nil
}()

extension BaseFeedViewController: UIScrollViewDelegate {

func scrollViewDidScroll(_ scrollView: UIScrollView) {

    let offset = scrollView.contentOffset.x
    let bounds = scrollView.bounds.width
    let page = CGFloat(self.currentPage)
    let count = CGFloat(viewControllers.count)
    let percentage = (offset - bounds + page * bounds) / (count * bounds - bounds)

    print(abs(percentage))
}
}

Answer 5

To make the code as readable and separated as possible, I would define an extension on UIPageViewController:

extension UIPageViewController {
  var scrollView: UIScrollView? {
    view.subviews.first(where: { $0 is UIScrollView }) as? UIScrollView
  }
}

It's quite easy to set yourself as the delegate for scroll view events, as so:

pageViewController.scrollView?.delegate = self

Answer 6

As of iOS 13, the UIPageViewController seems to reset the scrollview's contentOffset once it transitions to another view controller. Here is a working solution:

1. Find the child scrollView and set its delegate to self, as other answers suggested
2. Keep track of the current page index of the pageViewController:

var currentPageIndex = 0
// The pageViewController's viewControllers
let orderredViewControllers: [UIViewController] = [controller1, controller2, ...]

pageViewController.delegate = self

func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
    guard completed, let currentViewController = pageViewController.viewControllers?.first else { return }
    currentPageIndex = orderredViewControllers.firstIndex(of: currentViewController)!
}

3. Get the progress that ranges from 0 to 1

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let contentOffsetX = scrollView.contentOffset.x
    let width = scrollView.frame.size.width
    let offset = CGFloat(currentPageIndex) / CGFloat(orderredViewControllers.count - 1)
    let progress = (contentOffsetX - width) / width + offset
}