Zoomable CollectionView

ViewController.swift

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let collectionView = ZoomableCollectionView(frame:self.view.frame)
        self.view.addSubview(collectionView)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}

ZoomableCell.swift

import UIKit

class ZoomableCell: UICollectionViewCell {
    var imageView:UIImageView!
    var scrollView:UIScrollView!
    
    required init(coder aDecoder:NSCoder){
        super.init(coder: aDecoder)!
    }
    
    override init(frame:CGRect){
        super.init(frame:frame)
        
        setup()
    }
    
    func setup() {
        //スクロールビューを設置
        scrollView = UIScrollView()
        scrollView.frame = CGRect(x:0,y:0,width:self.frame.width,height:self.frame.height)
        
        //デリゲートを設定
        scrollView.delegate = self
        
        //最大・最小の大きさを決める
        scrollView.maximumZoomScale = 4.0
        scrollView.minimumZoomScale = 1.0
        
        self.contentView.addSubview(scrollView)
        
        //imageViewを生成
        imageView =  UIImageView()
        imageView.frame = CGRect(x:0,y:0,width:self.frame.width,height:self.frame.height)
        scrollView.addSubview(imageView)
        
        let doubleTap = UITapGestureRecognizer(target:self,action:#selector(self.doubleTap(gesture:)))
        doubleTap.numberOfTapsRequired = 2
        imageView.isUserInteractionEnabled = true
        imageView.addGestureRecognizer(doubleTap)
    }
    
    
    // ダブルタップ
    @objc func doubleTap(gesture: UITapGestureRecognizer){
        // if ( self.scrollView.zoomScale < self.scrollView.maximumZoomScale ) {
        if ( self.scrollView.zoomScale < 3 ) {
            let newScale:CGFloat = self.scrollView.zoomScale * 3
            let zoomRect:CGRect = 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)
        }
    }
    
    // 領域
    func zoomRectForScale(scale:CGFloat, center: CGPoint) -> CGRect{
        var zoomRect: CGRect = CGRect()
        zoomRect.size.height = self.scrollView.frame.size.height / scale
        zoomRect.size.width = self.scrollView.frame.size.width / scale
        
        zoomRect.origin.x = center.x - zoomRect.size.width / 2.0
        zoomRect.origin.y = center.y - zoomRect.size.height / 2.0
        
        return zoomRect
    }
}

extension ZoomableCell :UIScrollViewDelegate {
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return self.imageView
    }
    
    func scrollViewDidZoom(_ scrollView: UIScrollView) {
        print("zoomおわり")
    }
    
    func scrollViewWillBeginZooming(_ scrollView: UIScrollView, with view: UIView?) {
        print("zoomするよ")
    }
    
    
}

ZoomableCollectionView.swift

import UIKit

class ZoomableCollectionView: UICollectionView{
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
        super.init(frame: frame, collectionViewLayout: layout)
    }
    
    convenience init(frame: CGRect) {
        let layout = UICollectionViewFlowLayout()
        layout.itemSize = CGSize(width:frame.width,height:frame.width * 4 / 3)
        //スクロールの向き
        layout.scrollDirection = .horizontal
        layout.minimumLineSpacing = 0
        layout.minimumInteritemSpacing = 0
        layout.sectionInset = UIEdgeInsetsMake(0,0,0,0)
        
        self.init(frame: frame, collectionViewLayout: layout)
        
        setup()
    }
    
    func setup() {
        //デリゲートをつける
        self.delegate = self
        self.dataSource = self
        
        //カスタムセルを指定
        self.register(ZoomableCell.self, forCellWithReuseIdentifier: "singleCell")
        
        //スクロールバーを表示するかどうか
        self.showsHorizontalScrollIndicator = false
        self.showsVerticalScrollIndicator = false
        
        self.backgroundColor = UIColor.gray
        
        //ページングをするかどうか
        self.isPagingEnabled = true
    }

}

extension ZoomableCollectionView: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        print("タップ")
    }
}

extension ZoomableCollectionView: UICollectionViewDataSource {
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 10
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        //セルの設定
        let cell:ZoomableCell = collectionView.dequeueReusableCell(withReuseIdentifier: "singleCell", for: indexPath) as! ZoomableCell
        
        let image = UIImage(named:"image2.png")
        cell.imageView.image = image
        
        return cell
    }
}