PanZoomImageView-blog-1.swift

class PanZoomImageView: UIScrollView {
	
	private let imageView = UIImageView()
	override init(frame: CGRect) {
		super.init(frame: frame)
		commonInit()
	}

	required init?(coder: NSCoder) {
    		super.init(coder: coder)
    		commonInit()
	}

	private func commonInit() {
		imageView.translatesAutoresizingMaskIntoConstraints = false
		imageView.contentMode = .scaleAspectFit
	  	addSubview(imageView)
    		NSLayoutConstraint.activate([
	    		imageView.widthAnchor.constraint(equalTo: widthAnchor),
      			imageView.heightAnchor.constraint(equalTo: heightAnchor),
      			imageView.centerXAnchor.constraint(equalTo: centerXAnchor),
      			imageView.centerYAnchor.constraint(equalTo: centerYAnchor)
		])
	}
} 

PanZoomImageView-blog-2.swift

private func commonInit() {
	// Setup image view
	// ...

	// Setup scroll view
	minimumZoomScale = 1
  	maximumZoomScale = 3
  	showsHorizontalScrollIndicator = false
  	showsVerticalScrollIndicator = false
  	delegate = self
}

PanZoomImageView-blog-3.swift

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

}

PanZoomImageView-blog-4.swift

@IBInspectable
private var imageName: String? {
	didSet {
		guard let imageName = imageName else {
			return
		}
		imageView.image = UIImage(named: imageName)
	}
}

PanZoomImageView-blog-5.swift

convenience init(named: String) {
	self.init(frame: .zero)
	self.imageName = named
}

PanZoomImageView-blog-6.swift

let myView = PanZoomImageView(named: "image-name")

PanZoomImageView-blog-7.swift

class PanZoomImageView: UIScrollView {

    @IBInspectable
    private var imageName: String? {
        didSet {
            guard let imageName = imageName else {
                return
            }
            imageView.image = UIImage(named: imageName)
        }
    }
    private let imageView = UIImageView()

    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }

    convenience init(named: String) {
        self.init(frame: .zero)
        self.imageName = named
    }

    private func commonInit() {
        // Setup image view
        imageView.translatesAutoresizingMaskIntoConstraints = false
        imageView.contentMode = .scaleAspectFit
        addSubview(imageView)
        NSLayoutConstraint.activate([
            imageView.widthAnchor.constraint(equalTo: widthAnchor),
            imageView.heightAnchor.constraint(equalTo: heightAnchor),
            imageView.centerXAnchor.constraint(equalTo: centerXAnchor),
            imageView.centerYAnchor.constraint(equalTo: centerYAnchor)
        ])

        // Setup scroll view
        minimumZoomScale = 1
        maximumZoomScale = 3
        showsHorizontalScrollIndicator = false
        showsVerticalScrollIndicator = false
        delegate = self
    }

}

extension PanZoomImageView: UIScrollViewDelegate {

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

}

PanZoomImageView-blog-8.swift

private func commonInit() {
	// Setup image view
	// ...

	// Setup scroll view
	// ...

	// Setup tap gesture
	let doubleTapRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleDoubleTap(_:)))
	doubleTapRecognizer.numberOfTapsRequired = 2
	addGestureRecognizer(doubleTapRecognizer)
}

@objc private func handleDoubleTap(_ sender: UITapGestureRecognizer) {
	if zoomScale == 1 {
		setZoomScale(2, animated: true)
	} else {
		setZoomScale(1, animated: true)
	}
}