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最佳答案

I decided to add the imageView to a UIScrollView. It allows the user to zoom and pan over. Here is the code I used.

in order to set max/min zoom I used :

    scrollImg.minimumZoomScale = 1.0
scrollImg.maximumZoomScale = 10.0

here is the rest of the code.

    var vWidth = self.view.frame.width
var vHeight = self.view.frame.height


var scrollImg: UIScrollView = UIScrollView()
scrollImg.delegate = self
scrollImg.frame = CGRectMake(0, 0, vWidth!, vHeight!)
scrollImg.backgroundColor = UIColor(red: 90, green: 90, blue: 90, alpha: 0.90)
scrollImg.alwaysBounceVertical = false
scrollImg.alwaysBounceHorizontal = false
scrollImg.showsVerticalScrollIndicator = true
scrollImg.flashScrollIndicators()


scrollImg.minimumZoomScale = 1.0
scrollImg.maximumZoomScale = 10.0


defaultView!.addSubview(scrollImg)


imageView!.layer.cornerRadius = 11.0
imageView!.clipsToBounds = false
scrollImg.addSubview(imageView!)

I also had to add this as well

func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
return self.imageView
}

Swift 3 & above function prototype

func viewForZooming(in scrollView: UIScrollView) -> UIView? {
return self.mainImage
}

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In my view, the problem is your determination of currentScale. It always equals 1, because you change the scale of your imageView. You should assign your currentScale as follows:

let currentScale = self.imageView?.frame.size.width / self.imageView?.bounds.size.width

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You can use ImageScrollView open source, a zoomable and scrollable image view. http://github.com/huynguyencong/ImageScrollView

Like this opensource, add ImageView to ScrollView

open class ImageScrollView: UIScrollView {
var zoomView: UIImageView? = nil
}


extension ImageScrollView: UIScrollViewDelegate{


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


public func scrollViewDidZoom(_ scrollView: UIScrollView) {
adjustFrameToCenter()
}
}

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UIImageView pinch zoom with UIScrollView || image zooming ios in swift 3 and Xcode 8 letter Youtube video URL

set uiscrollview Delegate in storyboard

 class PhotoDetailViewController: UIViewController, UIScrollViewDelegate {


@IBOutlet weak var scrollView: UIScrollView!
@IBOutlet weak var imgPhoto: UIImageView!
      

override func viewDidLoad() {
        

super.viewDidLoad()
    

scrollView.minimumZoomScale = 1.0
scrollView.maximumZoomScale = 6.0
// scrollView.delegate = self - it is set on the storyboard.
}
        

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

return imgPhoto
}

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I think the biggest problem is at the end of your func, you have sender.scale = 1. If you remove that line of code, your image shouldn't just bounce back each time.

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Swift 3 solution

By default UIImageView's userInteration is disabled. Enable it before adding any gestures in UIImageView.

imgView.isUserInteractionEnabled = true

The scale factor relative to the points of the two touches in screen coordinates

var lastScale:CGFloat!
func zoom(gesture:UIPinchGestureRecognizer) {
if(gesture.state == .began) {
// Reset the last scale, necessary if there are multiple objects with different scales
lastScale = gesture.scale
}
if (gesture.state == .began || gesture.state == .changed) {
let currentScale = gesture.view!.layer.value(forKeyPath:"transform.scale")! as! CGFloat
// Constants to adjust the max/min values of zoom
let kMaxScale:CGFloat = 2.0
let kMinScale:CGFloat = 1.0
var newScale = 1 -  (lastScale - gesture.scale)
newScale = min(newScale, kMaxScale / currentScale)
newScale = max(newScale, kMinScale / currentScale)
let transform = (gesture.view?.transform)!.scaledBy(x: newScale, y: newScale);
gesture.view?.transform = transform
lastScale = gesture.scale  // Store the previous scale factor for the next pinch gesture call
}
}

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Swift 3 solution

This is the code I used. I added imageView to scrollView as a subview.

class ZoomViewController: UIViewController,UIScrollViewDelegate {


@IBOutlet weak var scrollView:UIScrollView!
@IBOutlet weak var imageView:UIImageView!


override func viewDidLoad() {


super.viewDidLoad()
scrollView.delegate = self


scrollView.minimumZoomScale = 1.0
scrollView.maximumZoomScale = 10.0//maximum zoom scale you want
scrollView.zoomScale = 1.0


}


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

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The option for swift 4

class ViewController: UIViewController, UIScrollViewDelegate {


@IBOutlet weak var scrolView: UIScrollView!
@IBOutlet weak var imgPhoto: UIImageView!


override func viewDidLoad() {
super.viewDidLoad()
scrolView.delegate = self
scrolView.minimumZoomScale = 1.0
scrolView.maximumZoomScale = 10.0
}


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

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This is an old question but I don't see any answers that explain what is wrong with the original code.

This line:

let currentScale = self.view.frame.size.width / self.view.bounds.size.width

Is working on the main view rather than the imageView so the scale calculation is always ~1

This simple change makes it behave as expected

let currentScale = sender.view!.frame.size.width / sender.view!.bounds.size.width

by changing self to sender (and forcing view to unwrap) the scale calculation works as expected.

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I ended up here, probably searching the wrong way.

I was after having my imageView in contentMode = .centre. But I was judging it too zoomed in and I was searching a way to zoom it out. Here's how:

    self.imageView.contentScaleFactor = 3

1 is as if you were doing anything. More that 1 zooms out... 3 works for me but you need to test it out.

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Using Swift 5.0, here is how it works for me:

let myImageView = UIImageView(image: myImage)
myImageView.isUserInteractionEnabled = true
let pinchMethod = UIPinchGestureRecognizer(target: self, action: #selector(pinchImage(sender:)))
myImageView.addGestureRecognizer(pinchMethod)


@objc func pinchImage(sender: UIPinchGestureRecognizer) {
guard let sender = sender.view else { return }


if let scale = (sender.view?.transform.scaledBy(x: sender.scale, y: sender.scale)) {
guard scale.a > 1.0 else { return }
guard scale.d > 1.0 else { return }
sender.view?.transform = scale
sender.scale = 1.0
}
}

You can use scale.a, scale.b, scale.c, scale.d, scale.tx and scale.ty to set your scale limits.

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Supporting Swift 5.1, You can create an extension of UIImageView, like this:

extension UIImageView {
func enableZoom() {
let pinchGesture = UIPinchGestureRecognizer(target: self, action: #selector(startZooming(_:)))
isUserInteractionEnabled = true
addGestureRecognizer(pinchGesture)
}


@objc
private func startZooming(_ sender: UIPinchGestureRecognizer) {
let scaleResult = sender.view?.transform.scaledBy(x: sender.scale, y: sender.scale)
guard let scale = scaleResult, scale.a > 1, scale.d > 1 else { return }
sender.view?.transform = scale
sender.scale = 1
}
}

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[September 2022, Swift 5]

One of the ways It seems to be working fine for me was embedding the image view into a scroll view which you can have a quick look at the library I'm sharing for better understanding to keep this answer short. I have built up this small library and used it in production apps. You can install or just copy-paste the files into your project. It is very easy to work with as an UIView and listen to its delegate for more options if you need them.

The library is called InteractiveImageView, it supports iOS 11.0 and up, link to GitHub: https://github.com/egzonpllana/InteractiveImageView