UIImageView which can zoom by pinch and double tap.

zoomByPinchDoubleTap.swift

//
//  ViewController.swift
//  pinchZoomImageVIewStudy
//

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var scrollView: UIScrollView!
    @IBOutlet weak var imageView: UIImageView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        scrollView.delegate = self
        scrollView.minimumZoomScale = 1.0
        scrollView.maximumZoomScale = 4.0
        
        setupGesture()
        
        if let image = UIImage(named: "myImage") {
            imageView.image = image
        }
        
    }


}

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

extension ViewController {
    func setupGesture() {
        let recognizer = UITapGestureRecognizer(target: self,
                                                action: #selector(onDoubleTap(_:)))
        recognizer.numberOfTapsRequired = 2
        scrollView.addGestureRecognizer(recognizer)
    }
    
    @objc func onDoubleTap(_ sender: UITapGestureRecognizer) {
        let scale = min(scrollView.zoomScale * 2, scrollView.maximumZoomScale)
        
        if scale != scrollView.zoomScale {
            let tapPoint = sender.location(in: imageView)
            let size = CGSize(width: scrollView.frame.size.width / scale,
                              height: scrollView.frame.size.height / scale)
            let origin = CGPoint(x: tapPoint.x - size.width / 2,
                                 y: tapPoint.y - size.height / 2)
            scrollView.zoom(to: CGRect(origin: origin, size: size), animated: true)
        }
        else {
            scrollView.zoom(to: scrollView.frame, animated: true)
        }
    }
}