Unable to zoom UIImageView in UIScrollView

Question

I want to zoom UIImageView in ScrollView but I do not know how to do this.

import UIKit

class ViewController: UIViewController, UIScrollViewDelegate {

    var scrollView: UIScrollView = UIScrollView()
    var viewInScrollView: UIView = UIView()
    var selectedImageView: UIImageView = UIImageView()


    override func viewDidLoad() {
        super.viewDidLoad()

        scrollView.delegate = self

        view.addSubview(scrollView)
        scrollView.addSubview(viewInScrollView)
        viewInScrollView.addSubview(selectedImageView)
        selectedImageView.image = UIImage(named: "michael")

        scrollView.translatesAutoresizingMaskIntoConstraints = false
        viewInScrollView.translatesAutoresizingMaskIntoConstraints = false
        selectedImageView.translatesAutoresizingMaskIntoConstraints = false

        scrollView.anchor(top: view.safeAreaLayoutGuide.topAnchor, leading: view.leadingAnchor, bottom: view.bottomAnchor, trailing: view.trailingAnchor)
        viewInScrollView.anchor(top: view.safeAreaLayoutGuide.topAnchor, leading: view.leadingAnchor, bottom: view.bottomAnchor, trailing: view.trailingAnchor)
        viewInScrollView.widthAnchor.constraint(equalToConstant: view.frame.width).isActive = true
        viewInScrollView.heightAnchor.constraint(equalToConstant: view.frame.height).isActive = true

        selectedImageView.anchor(top: viewInScrollView.topAnchor, leading: viewInScrollView.leadingAnchor, bottom: viewInScrollView.bottomAnchor, trailing: viewInScrollView.trailingAnchor)

    }

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

}

Answer 1

I suggest to start with a tutorial example for UIScrollView zooming. Do it step by step first.

And ....

At a glance, your constraints for viewInScrollView are not accurate. The views hierarchy in your project is

view -> scrollView -> viewInScrollView -> selectedImageView

The constraints for viewInScrollView will decide the contentSize of UIScrollView . When zooming in/zooming out, the contentSize will changed. So, it's (top, bottom, left, right) anchor should aligned to UIScrollView , not to view . So I think the following constraint is wrong.

// Not right
viewInScrollView.anchor(top: view.safeAreaLayoutGuide.topAnchor, leading: view.leadingAnchor, bottom: view.bottomAnchor, trailing: view.trailingAnchor)

// It should aligned to `UIScrollView`'s top, bottom, left and right anchors.

Answer 2

You have to add maximumZoomScale , minimumZoomScale to your scrollView like following.

scrollView.minimumZoomScale = 0.25
scrollView.maximumZoomScale = 5.0

Hope this help!.