How to enable zoom in UIScrollView

Solution 1:

Answer is here:

A scroll view also handles zooming and panning of content. As the user makes a pinch-in or pinch-out gesture, the scroll view adjusts the offset and the scale of the content. When the gesture ends, the object managing the content view should update subviews of the content as necessary. (Note that the gesture can end and a finger could still be down.) While the gesture is in progress, the scroll view does not send any tracking calls to the subview.

The UIScrollView class can have a delegate that must adopt the UIScrollViewDelegate protocol. For zooming and panning to work, the delegate must implement both viewForZoomingInScrollView: and scrollViewDidEndZooming:withView:atScale:; in addition, the maximum (maximumZoomScale) and minimum (minimumZoomScale) zoom scale must be different.

So:

1. You need a delegate that implements UIScrollViewDelegate and is set to delegate on your UIScrollView instance
2. On your delegate you have to implement one method: viewForZoomingInScrollView: (which must return the content view you're interested in zooming). You can also implement scrollViewDidEndZooming:withView:atScale: optionally.
3. On your UIScrollView instance, you have to set the minimumZoomScale and the maximumZoomScale to be different (they are 1.0 by default).

Note: The interesting thing about this is what if you want to break zooming. Is it enough to return nil in the viewForZooming... method? It does break zooming, but some of the gestures will be messed up (for two fingers). Therefore, to break zooming you should set the min and max zoom scale to 1.0.

Solution 2:

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.

Solution 3:

Make sure you set your viewController as the scrollViews delegate and implement:

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