Simliar to iOS Photos App where the user is zooming in and out of an image by pinching:
UIView > UIScrollView > UIImageView > UIImage
Initially, I had the issue
for swift 4
func scrollViewDidZoom(_ scrollView: UIScrollView) {
if scrollView.zoomScale > 1 {
if let image = self.imageViewZoom.image {
let ratioW = self.imageViewZoom.frame.width / image.size.width
let ratioH = self.imageViewZoom.frame.height / image.size.height
let ratio = ratioW < ratioH ? ratioW:ratioH
let newWidth = image.size.width*ratio
let newHeight = image.size.height*ratio
let left = 0.5 * (newWidth * scrollView.zoomScale > self.imageViewZoom.frame.width ? (newWidth - self.imageViewZoom.frame.width) : (scrollView.frame.width - scrollView.contentSize.width))
let top = 0.5 * (newHeight * scrollView.zoomScale > self.imageViewZoom.frame.height ? (newHeight - self.imageViewZoom.frame.height) : (scrollView.frame.height - scrollView.contentSize.height))
scrollView.contentInset = UIEdgeInsetsMake(top, left, top, left)
}
} else {
scrollView.contentInset = UIEdgeInsets.zero
}
}
Swift 5
func scrollViewDidZoom(_ scrollView: UIScrollView) {
if scrollView.zoomScale > 1 {
if let image = imageView.image {
let ratioW = imageView.frame.width / image.size.width
let ratioH = imageView.frame.height / image.size.height
let ratio = ratioW < ratioH ? ratioW : ratioH
let newWidth = image.size.width * ratio
let newHeight = image.size.height * ratio
let left = 0.5 * (newWidth * scrollView.zoomScale > imageView.frame.width ? (newWidth - imageView.frame.width) : (scrollView.frame.width - scrollView.contentSize.width))
let top = 0.5 * (newHeight * scrollView.zoomScale > imageView.frame.height ? (newHeight - imageView.frame.height) : (scrollView.frame.height - scrollView.contentSize.height))
scrollView.contentInset = UIEdgeInsets(top: top, left: left, bottom: top, right: left)
}
} else {
scrollView.contentInset = UIEdgeInsets.zero
}
}
Your approach looks correct. You need to update your code as below.
func scrollViewDidZoom(scrollView: UIScrollView) {
if scrollView.zoomScale > 1 {
if let image = imageView.image {
let ratioW = imageView.frame.width / image.size.width
let ratioH = imageView.frame.height / image.size.height
let ratio = ratioW < ratioH ? ratioW:ratioH
let newWidth = image.size.width*ratio
let newHeight = image.size.height*ratio
let left = 0.5 * (newWidth * scrollView.zoomScale > imageView.frame.width ? (newWidth - imageView.frame.width) : (scrollView.frame.width - scrollView.contentSize.width))
let top = 0.5 * (newHeight * scrollView.zoomScale > imageView.frame.height ? (newHeight - imageView.frame.height) : (scrollView.frame.height - scrollView.contentSize.height))
scrollView.contentInset = UIEdgeInsetsMake(top, left, top, left)
}
} else {
scrollView.contentInset = UIEdgeInsetsZero
}
}