Calling 'scrollView.zoom' Does Not Zoom - ios

Question

For some reason scrollView.zoom does not zoom in on an imageView.
I have an imageView inside a scrollView.
in ViewDidLoad:
scrollView.minimumZoomScale = 1.0
scrollView.maximumZoomScale = 2.0
scrollView.delegate = self
viewForZooming:
func viewForZooming(in scrollView: UIScrollView) -> UIView? {
return imageView
}
Now, I'm calling below after both scrollView and imageView are initialized.
var scale: CGFloat = 2
let location = CGPoint(x: imageView.frame.width/2, y: imageView.frame.height/2)
scrollView.zoom(to: zoomRectForScale(scale, center: location), animated: true)
Nothing is happening after scrollView.zoom is called. I tried doing
view.setNeedsDisplay()
view.layoutIfNeeded()
Still nothing happens, imageView is not zooming in.
UPDATE:
As requested, here is the code for scrollView and imageView initialization:
func createscrollView(image: UIImage?){
if image == nil{
let img = UIImage(named: "demo image.jpg")
let imgCorrected = scaleAndOrient(image: img!)
//created user selecged images
userSelectedImage_UI = img
userSelectedImage_UI_Corrected = imgCorrected
}
// create image scroll view
scrollView = UIScrollView(frame: CGRect(x: 0, y: 0,width: 100, height: 100))
scrollView.showsHorizontalScrollIndicator = false
scrollView.showsVerticalScrollIndicator = false
scrollView.bouncesZoom = false
scrollView.bounces = false
scrollView.contentMode = .scaleAspectFill
view.addSubview(scrollView)
scrollView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
scrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 0),
scrollView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor, constant: 0),
scrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -150),
scrollView.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor, constant: 0)
])
// add image view to scrollview
imageView = UIImageView(frame: CGRect(x: 0, y: 0,width: 100, height: 100))
scrollView.addSubview(imageView)
imageView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
imageView.topAnchor.constraint(equalTo: scrollView.contentLayoutGuide.topAnchor, constant: 0),
imageView.leftAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leftAnchor, constant: 0),
imageView.bottomAnchor.constraint(equalTo: scrollView.contentLayoutGuide.bottomAnchor, constant: 0),
imageView.rightAnchor.constraint(equalTo: scrollView.contentLayoutGuide.rightAnchor, constant: 0),
imageView.widthAnchor.constraint(equalTo: scrollView.widthAnchor, multiplier: 1),
imageView.heightAnchor.constraint(equalTo: scrollView.heightAnchor, multiplier: 1)
])
imageView.contentMode = .scaleAspectFit
if image == nil{
imageView.image = userSelectedImage_UI_Corrected
} else {
imageView.image = scaleAndOrient(image: image!)
}
}

Answer 1

Based on comments...
It sounds like you are creating / setting up your scrollView and its content imageView from viewDidLoad() and then immediately trying to "zoom" it.
If so, that will be problematic, as auto-layout hasn't finished laying out the UI elements.
You can call it from:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
var scale: CGFloat = 2
let location = CGPoint(x: imageView.frame.width/2, y: imageView.frame.height/2)
scrollView.zoom(to: zoomRectForScale(scale, center: location), animated: true)
}

Answer 2

I have a feeling the problem is in your zoomRectForScale function, though it isn't posted. It should be something like this:
func zoomRectForScale(_ scale: CGFloat, center: CGPoint) -> CGRect {
var zoomRect = CGRect.zero
zoomRect.size.height = imageView.frame.size.height / scale
zoomRect.size.width = imageView.frame.size.width / scale
let newCenter = scrollView.convert(center, from: imageView)
zoomRect.origin.x = newCenter.x - (zoomRect.size.width / 2.0)
zoomRect.origin.y = newCenter.y - (zoomRect.size.height / 2.0)
return zoomRect
}
Additionally, I've verified that double-tapping to zoom works to the correct location using:
var gestureRecognizer: UITapGestureRecognizer!
// Sets up the gesture recognizer that receives double taps to auto-zoom
func setupGestureRecognizer() {
gestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleDoubleTap))
gestureRecognizer.numberOfTapsRequired = 2
scrollView.addGestureRecognizer(gestureRecognizer)
}
// Handles a double tap by either resetting the zoom or zooming to where was tapped
#IBAction func handleDoubleTap() {
if scrollView.zoomScale == 1 {
scrollView.zoom(to: zoomRectForScale(scrollView.maximumZoomScale, center: gestureRecognizer.location(in: gestureRecognizer.view)), animated: true)
} else {
scrollView.setZoomScale(1, animated: true)
}
}
Don't forget to call this in viewDidLoad:
setupGestureRecognizer()
If this doesn't solve your issue, please adjust your question with missing code functions and variable declarations.