UIScrollView zooming with Auto Layout

Question

I\'m trying to implement a UIScrollView the New Way, using Auto Layout. I\'ve set up constraints from the inner view to the scroll view so that it can compute i

Answer 1

Complete Swift Playground Example

The simplest example I can think of is adding a UIImageView to a UIScrollView. This is 100% in code, you'll just need to add a PNG to the Playground. I called mine Image.png. In a Playground you'll see the whole thing rendered in the 'Live View'. Pinch-zoom works using a Ctrl-click to place one finger on the screen and then dragging around. Until the content is zoomed in bigger than the screen panning will not work. Double-tap the image to toggle between 1x and 3x scale.

Based upon the Apple's Technical Note TN2154: UIScrollView and Autolayout

Gotcha

You'll find the whole thing very frustrating if your content is not bigger than the screen size. If your content completely fits on screen nothing will happen. That's why you must get zooming to work too. If you want to prove to yourself it works, test with a really big image (bigger than the window).

import UIKit
import PlaygroundSupport

enum TapToggle {
    case Regular, Large
}

class ScrollingViewController : UIViewController
{
    var tapToggle: TapToggle = .Large
    var scrollView: UIScrollView?
    var imageView: UIImageView?

    override func viewDidLoad()
    {
        let image = UIImage(named: "Image")
        let imageView = UIImageView(image: image)
        imageView.translatesAutoresizingMaskIntoConstraints = false
        imageView.backgroundColor = .white
        imageView.isUserInteractionEnabled = true

        let scrollView = UIScrollView()
        scrollView.minimumZoomScale = 0.5
        scrollView.maximumZoomScale = 10.0
        scrollView.delegate = self
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.addSubview(imageView)
        let imageViewKey = "imageView"
        let imageViews = [imageViewKey: imageView]
        scrollView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[\(imageViewKey)]|", options: [], metrics: nil, views: imageViews))
        scrollView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[\(imageViewKey)]|", options: [], metrics: nil, views: imageViews))
        self.imageView = imageView

        scrollView.backgroundColor = .white
        self.view.addSubview(scrollView)

        let scrollViewKey = "scrollView"
        let scrollViews = [scrollViewKey: scrollView]
        self.view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[\(scrollViewKey)]|", options: [], metrics: nil, views: scrollViews))
        self.view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[\(scrollViewKey)]|", options: [], metrics: nil, views: scrollViews))

        self.scrollView = scrollView

        let tapGesture = UITapGestureRecognizer(target: self, action: #selector(didDoubleTap(sender:)))
        tapGesture.numberOfTapsRequired = 2
        self.imageView?.addGestureRecognizer(tapGesture)
    }

    @objc
    public func didDoubleTap(sender: AnyObject)
    {
        switch self.tapToggle {
        case .Regular:
            self.scrollView?.zoomScale = 1.0
            self.tapToggle = .Large
        case .Large:
            self.scrollView?.zoomScale = 3.0
            self.tapToggle = .Regular
        }
    }
}

extension ScrollingViewController: UIScrollViewDelegate
{
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return self.imageView
    }

    func scrollViewDidEndZooming(_ scrollView: UIScrollView, with view: UIView?, atScale scale: CGFloat)
    {
        print("\(scale)")
    }
}

PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.liveView = ScrollingViewController()