How to enable zoom in UIScrollView

Question

How do I enable zooming in a UIScrollView?

Answer 1

Have a read through this Ray Wenderlich tutorial:

http://www.raywenderlich.com/76436/use-uiscrollview-scroll-zoom-content-swift

If you follow through the section 'Scrolling and Zooming a Larger Image' it will get a image up and enable you to pinch and zoom.

In case the link gets altered, here's the main info: Put this code in your view controller (this sets the main functionality):

override func viewDidLoad() {
  super.viewDidLoad()

  // 1
  let image = UIImage(named: "photo1.png")!
  imageView = UIImageView(image: image)
  imageView.frame = CGRect(origin: CGPoint(x: 0, y: 0), size:image.size)
  scrollView.addSubview(imageView)

  // 2
  scrollView.contentSize = image.size

  // 3
  var doubleTapRecognizer = UITapGestureRecognizer(target: self, action: "scrollViewDoubleTapped:")
  doubleTapRecognizer.numberOfTapsRequired = 2
  doubleTapRecognizer.numberOfTouchesRequired = 1
  scrollView.addGestureRecognizer(doubleTapRecognizer)

  // 4
  let scrollViewFrame = scrollView.frame
  let scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
  let scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
  let minScale = min(scaleWidth, scaleHeight);
  scrollView.minimumZoomScale = minScale;

  // 5
  scrollView.maximumZoomScale = 1.0
  scrollView.zoomScale = minScale;

  // 6
  centerScrollViewContents()
}

Add this to the class:

func centerScrollViewContents() {
  let boundsSize = scrollView.bounds.size
  var contentsFrame = imageView.frame

  if contentsFrame.size.width < boundsSize.width {
    contentsFrame.origin.x = (boundsSize.width - contentsFrame.size.width) / 2.0
  } else {
    contentsFrame.origin.x = 0.0
  }

  if contentsFrame.size.height < boundsSize.height {
    contentsFrame.origin.y = (boundsSize.height - contentsFrame.size.height) / 2.0
  } else {
    contentsFrame.origin.y = 0.0
  }

  imageView.frame = contentsFrame
}

And then this if you want the double tap gesture to be recognised:

func scrollViewDoubleTapped(recognizer: UITapGestureRecognizer) {
  // 1        
  let pointInView = recognizer.locationInView(imageView)

  // 2
  var newZoomScale = scrollView.zoomScale * 1.5
  newZoomScale = min(newZoomScale, scrollView.maximumZoomScale)

  // 3
  let scrollViewSize = scrollView.bounds.size
  let w = scrollViewSize.width / newZoomScale
  let h = scrollViewSize.height / newZoomScale
  let x = pointInView.x - (w / 2.0)
  let y = pointInView.y - (h / 2.0)

  let rectToZoomTo = CGRectMake(x, y, w, h);

  // 4
  scrollView.zoomToRect(rectToZoomTo, animated: true)
}

If you want more detail read the tutorial, but that pretty much covers it.