Image Zoom not working in a UIScrollView inside a Root UIScrollView

Question

I'm trying to zoom an image that is inside a UIScrollView, and that UIScrollView it's inside of a root UIScrollView that allow paging, similar to the Photos app.

In the viewDidLoad() inside the view that contains the root scrollView I call prepareScrollView()

    func prepareScrollView(){

      let tap = UITapGestureRecognizer(target: self, action: #selector(hideNavigationItem))


      scrollView.addGestureRecognizer(tap)

      scrollView.delegate = self
      scrollView.minimumZoomScale = 1.0
      scrollView.maximumZoomScale = 4.0
      scrollView.zoomScale = 1.0


      let width = self.view.bounds.width
      let height = self.view.bounds.height
      totalWidth = width * CGFloat((imageArray!.count)!) //The width must be the width of the screen by the number of the images in the array
      scrollView.contentSize = CGSize(width: totalWidth, height: height)
      scrollView.isPagingEnabled = true

      loadPages()

}

The loadPages() function load every scrollView with their image and add it to the root scrollview.

func loadPages(){

    for i in 0...((imageArray!.count)! - 1){

        let pageScroll = Page(frame: CGRect(x: self.view.bounds.size.width * CGFloat(i), y: self.view.frame.origin.y, width: self.view.bounds.size.width, height: self.view.bounds.size.height))

        pageScroll.minimumZoomScale = 1.0
        pageScroll.maximumZoomScale = 4.0
        pageScroll.zoomScale = 1.0

        let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: self.view.bounds.size.width, height: self.view.bounds.size.height))
        imageView.image = UIImage(data: (imageArray![i])!)
        imageView.contentMode = .scaleToFill
        pageScroll.addSubview(imageView)

        scrollView.addSubview(pageScroll)
    }
}

The Page object it's just a UIScrollView object.

class Page: UIScrollView {
func viewForZooming(in scrollView: UIScrollView) -> UIView? {
    return self.subviews[0]//Return the image
}

}

And inside the root scrollView viewForZooming function it calls the viewForZooming function of the correspond child scrollview.

func viewForZooming(in scrollView: UIScrollView) -> UIView? {

    if(self.scrollView.subviews.count > 0){
        let childScrollView = self.scrollView.subviews[currentPage] as! Page
        let image = childScrollView.viewForZooming(in: scrollView)
        return image
    }
    return nil
}

With this approach I can navigate horizontally but I can't zoom in the current image. The viewForZooming function executes in both objects. What I'm doing wrong?

Try disabling zooming in the outer scroll view. It could be the case that the outer scroll view tries to zoom but fails. — Vlad Rusu

F.Stan F.Stan · Accepted Answer · 2020-03-27T18:01:39

Finally I solve my issue. I changed the Page object to a simple UIScrollView and then set the delegate of the scrollView object to self.

func loadPages(){

    for i in 0...((comic?.comicsPages!.count)! - 1){

        let pageScroll = UIScrollView(frame: CGRect(x: self.view.bounds.size.width * CGFloat(i), y: self.view.frame.origin.y, width: self.view.bounds.size.width, height: self.view.bounds.size.height))

        pageScroll.minimumZoomScale = 1.0
        pageScroll.maximumZoomScale = 4.0
        pageScroll.zoomScale = 1.0
        pageScroll.isUserInteractionEnabled = true
        pageScroll.delegate = self //Here

        let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: self.view.bounds.size.width, height: self.view.bounds.size.height))
        imageView.image = UIImage(data: (imageArray![i])!)
        imageView.contentMode = .scaleToFill

        pageScroll.addSubview(imageView)

        scrollView.addSubview(pageScroll)
    }
}

And then in the viewForZooming function of the root scrollView I change the code for this:

func viewForZooming(in scrollView: UIScrollView) -> UIView? {

    if(scrollView.subviews.count > 0){
        return scrollView.subviews[0]
    }
    return nil
}

The scrollView parameter is the child scrollview so it works as expected.

Image Zoom not working in a UIScrollView inside a Root UIScrollView

1 Answers