UIScrollView Zooming & contentInset

Question

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

Answer 1

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
    }
}