Gesture Image Zoom View Controller

GestureImageZoomViewController.swift

//
//    GestureImageZoomViewController.swift
//    
//    Created by Ytse Jam on 2017/10/21.
//    Copyright © 2017 Ytse Jam. Licensed under MIT.
//

import UIKit

class GestureImageZoomViewController: UIViewController, UIScrollViewDelegate {
    // ***** Important *****
    // Need to set UIImageView as a child of UIScrollView on Storyboad
    @IBOutlet var imageView: UIImageView!
    @IBOutlet var scrollView: UIScrollView!
    
    var params = SelectionParameters()
    var image: UIImage? = nil

    override func viewDidLoad() {
        super.viewDidLoad()
        
        imageView.image = self.image
        
        self.scrollView.delegate = self

        // ***** Important *****
        // Need to checkbox ON.(Storyboad:Attributes inspector -> View -> Intaraction -> User Intaraction Enabled -> True)
        // Need to set values below.
        //   Storyboad:Attributes inspector -> Scroll View -> Zoom -> Min & Max
        let doubleTapGesture = UITapGestureRecognizer(target: self, action: #selector(self.doubleTap))
        doubleTapGesture.numberOfTapsRequired = 2
        self.imageView.addGestureRecognizer(doubleTapGesture)
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
    
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return self.imageView
    }
    
    @objc func doubleTap(gesture: UITapGestureRecognizer) -> Void {
        if (self.scrollView.zoomScale < self.scrollView.maximumZoomScale) {
            let newScale = self.scrollView.zoomScale * 3
            let zoomRect = self.zoomRectForScale(scale: newScale, center: gesture.location(in: gesture.view))
            self.scrollView.zoom(to: zoomRect, animated: true)
        } else {
            self.scrollView.setZoomScale(1.0, animated: true)
        }
    }
    
    func zoomRectForScale(scale:CGFloat, center: CGPoint) -> CGRect{
        let size = CGSize(
            width: self.scrollView.frame.size.width / scale,
            height: self.scrollView.frame.size.height / scale
        )
        return CGRect(
            origin: CGPoint(
                x: center.x - size.width / 2.0,
                y: center.y - size.height / 2.0
            ),
            size: size
        )
    }
}