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

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
        }
    }