A UIScrollView with an UIImageView that enables zooming.

FullScreenImageView.swift

import UIKit
import Kingfisher

class FullScreenImageView: UIView {
    
    @IBOutlet var contentView: UIView!
    @IBOutlet var dismissButton: UIButton!
    @IBOutlet var shareButton: UIButton!
    @IBOutlet var imageView: UIImageView!
    @IBOutlet var scrollView: UIScrollView!
    @IBOutlet var imageViewTopConstraint: NSLayoutConstraint!
    @IBOutlet var imageViewBottomConstraint: NSLayoutConstraint!
    @IBOutlet var imageViewLeadingConstraint: NSLayoutConstraint!
    @IBOutlet var imageViewTrailingConstraint: NSLayoutConstraint!
    
    override init(frame: CGRect) {
        super.init(frame: UIScreen.main.bounds)
        commonInit()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        commonInit()
    }
    
    fileprivate func commonInit() {
        Bundle.main.loadNibNamed("FullScreenImageView", owner: self, options: nil)
        addSubview(contentView)
        contentView.frame = bounds
        contentView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        imageView.contentMode = .scaleAspectFit
        shareButton.setImage(UIImage(named: "shareIcon"), for: .normal)
        scrollView.delegate = self
        scrollView.maximumZoomScale = 6.0
        scrollView.minimumZoomScale = 1.0
    }
    
    public func configureView(_ photo: Photo) {
        guard let urlString = photo.url_m else {
            imageView.image = UIImage(named: "placeholderImage")
            return
        }
        if let image = ImageCache.default.retrieveImageInDiskCache(forKey: urlString) {
            imageView.image = image
        } else if let image = ImageCache.default.retrieveImageInMemoryCache(forKey: urlString) {
            imageView.image = image
        }
    }
}

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