CarouselView - Paging

CarouselCell.swift

//
//  CarouselCell.swift
//  CardCarousel2
//
//  Created by Reona Kubo on 2018/06/11.
//  Copyright © 2018年 Reona Kubo. All rights reserved.
//

import UIKit

class CarouselCell: UICollectionViewCell {
    
}

CarouselView.swift

//
//  CarouselView.swift
//  CardCarousel2
//
//  Created by Reona Kubo on 2018/06/11.
//  Copyright © 2018年 Reona Kubo. All rights reserved.
//

import UIKit

class CarouselView: UICollectionView {

    let cellIdentifier = "carousel"
    let pageCount = 5
    let colors:[UIColor] = [.blue,.yellow,.red,.green,.gray]
    let isInfinity = true
    var cellItemsWidth: CGFloat = 0.0
    
    var cellWidth:CGFloat = 200
    let windowWidth:CGFloat = UIScreen.main.bounds.width
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
        super.init(frame: frame, collectionViewLayout: layout)
        self.delegate = self
        self.dataSource = self
        self.register(CarouselCell.self, forCellWithReuseIdentifier: cellIdentifier)
    }
    
    convenience init(frame: CGRect) {
        let layout = PagingPerCellFlowLayout()
        layout.itemSize = CGSize(width: 200, height: frame.height / 2)
        layout.scrollDirection = .horizontal
        //layout.minimumLineSpacing = 0
        
        self.init(frame: frame, collectionViewLayout: layout)
        
        // 水平方向のスクロールバーを非表示にする
        self.showsHorizontalScrollIndicator = false
        self.backgroundColor = UIColor.white
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        // 画面内に表示されているセルを取得
        let cells = self.visibleCells
        for cell in cells {
            // ここでセルのScaleを変更する
            transformScale(cell: cell)
        }
        
    }
    
    // セルのスケールを変更する
    func transformScale(cell: UICollectionViewCell) {
        let cellCenter:CGPoint = self.convert(cell.center, to: nil) //セルの中心座標
        let screenCenterX:CGFloat = UIScreen.main.bounds.width / 2  //画面の中心座標x
        let reductionRatio:CGFloat = -0.0005                        //縮小率
        let maxScale:CGFloat = 1                                    //最大値
        let cellCenterDisX:CGFloat = abs(screenCenterX - cellCenter.x)   //中心までの距離
        let newScale = reductionRatio * cellCenterDisX + maxScale   //新しいスケール
        cell.transform = CGAffineTransform(scaleX:newScale, y:newScale)
    }
    
    // 初期位置を真ん中にする
    func scrollToFirstItem() {
        //self.layoutIfNeeded()
        if isInfinity {
            self.scrollToItem(at:IndexPath(row: self.pageCount, section: 0) , at: .centeredHorizontally, animated: false)
        }
    }
    
}

extension CarouselView: UICollectionViewDelegate {
    
}

extension CarouselView: UICollectionViewDataSource {
    
    // セクションごとのセル数
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return isInfinity ? pageCount * 3 : pageCount
    }
    
    // セルの設定
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell:CarouselCell = dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! CarouselCell
        
        configureCell(cell: cell, indexPath: indexPath)
        
        return cell
    }
    
    func configureCell(cell: CarouselCell,indexPath: IndexPath) {
        // indexを修正する
        let fixedIndex = isInfinity ? indexPath.row % pageCount : indexPath.row
        cell.contentView.backgroundColor = colors[fixedIndex]
    }
    
}

extension CarouselView: UIScrollViewDelegate {
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        
        if isInfinity {
            if cellItemsWidth == 0.0 {
                cellItemsWidth = floor(scrollView.contentSize.width / 3.0) // 表示したい要素群のwidthを計算
            }
            
            if (scrollView.contentOffset.x <= 0.0) || (scrollView.contentOffset.x > cellItemsWidth * 2.0) { // スクロールした位置がしきい値を超えたら中央に戻す
                scrollView.contentOffset.x = cellItemsWidth
            }
        }
        
    }
    
    /***** 方法3 ******/
//    //速度velocityを持っていてドラッグが終わりそうなとき。最終的な落ち着き先をtargetContentOffsetで指定
//    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
//
//        targetContentOffset.pointee = targetContentOffsetPoint(scrollView, velocity: velocity)
//    }
//
//    func targetContentOffsetPoint(_ scrollView: UIScrollView,velocity:CGPoint) -> CGPoint{
//        let cellWidth:CGFloat = 200
//        let windowWidth:CGFloat = UIScreen.main.bounds.width
//        var offsetAdjustment:CGFloat = CGFloat(MAXFLOAT)
//        let horizontalOffest:CGFloat = scrollView.contentOffset.x + ( windowWidth - cellWidth ) / 2
//
//        let targetRect = CGRect(x:scrollView.contentOffset.x + velocity.x * cellWidth,
//                                y:0,
//                                width:self.bounds.size.width,
//                                height:self.bounds.size.height)
//
//        let array = self.collectionViewLayout.layoutAttributesForElements(in: targetRect)
//
//        for layoutAttributes in array! {
//            let itemOffset = layoutAttributes.frame.origin.x
//            if abs(itemOffset - horizontalOffest) < abs(offsetAdjustment) {
//                offsetAdjustment = itemOffset - horizontalOffest
//            }
//        }
//        return CGPoint(x:scrollView.contentOffset.x + offsetAdjustment, y:scrollView.contentOffset.y)
//    }
    
}

PagingPerCellFlowLayout.swift

//
//  PagingPerCellFlowLayout.swift
//  CardCarousel2
//
//  Created by Reona Kubo on 2018/06/12.
//  Copyright © 2018年 Reona Kubo. All rights reserved.
//

import UIKit

class PagingPerCellFlowLayout: UICollectionViewFlowLayout {
    
    var cellWidth:CGFloat = 200
    let windowWidth:CGFloat = UIScreen.main.bounds.width
    
    /***** 方法1 ******/
    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
        
        var offsetAdjustment:CGFloat = CGFloat(MAXFLOAT)
        let horizontalOffest:CGFloat = proposedContentOffset.x + ( windowWidth - cellWidth ) / 2
        let targetRect = CGRect(x:proposedContentOffset.x,
                                y:0,
                                width:self.collectionView!.bounds.size.width,
                                height:self.collectionView!.bounds.size.height)
        
        let array = super.layoutAttributesForElements(in: targetRect)
        
        for layoutAttributes in array! {
            let itemOffset = layoutAttributes.frame.origin.x
            if abs(itemOffset - horizontalOffest) < abs(offsetAdjustment) {
                offsetAdjustment = itemOffset - horizontalOffest
            }
        }
        
        return CGPoint(x:proposedContentOffset.x + offsetAdjustment, y:proposedContentOffset.y)
    }
    
    /***** 方法2 ******/
//    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint
//    {
//        if let collectionViewBounds = self.collectionView?.bounds
//        {
//            let halfWidthOfVC = collectionViewBounds.size.width * 0.5
//            let proposedContentOffsetCenterX = proposedContentOffset.x + halfWidthOfVC
//            if let attributesForVisibleCells = self.layoutAttributesForElements(in: collectionViewBounds)
//            {
//                var candidateAttribute : UICollectionViewLayoutAttributes?
//                for attributes in attributesForVisibleCells
//                {
//                    let candAttr : UICollectionViewLayoutAttributes? = candidateAttribute
//                    if candAttr != nil
//                    {
//                        let a = attributes.center.x - proposedContentOffsetCenterX
//                        let b = candAttr!.center.x - proposedContentOffsetCenterX
//                        if fabs(a) < fabs(b)
//                        {
//                            candidateAttribute = attributes
//                        }
//                    }
//                    else
//                    {
//                        candidateAttribute = attributes
//                        continue
//                    }
//                }
//
//                if candidateAttribute != nil
//                {
//                    return CGPoint(x: candidateAttribute!.center.x - halfWidthOfVC, y: proposedContentOffset.y);
//                }
//            }
//        }
//        return CGPoint.zero
//    }
    
}

ViewController.swift

//
//  ViewController.swift
//  CardCarousel2
//
//  Created by Reona Kubo on 2018/06/11.
//  Copyright © 2018年 Reona Kubo. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    var carouselView:CarouselView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let width = self.view.frame.width
        let height = self.view.frame.height
        
        carouselView = CarouselView(frame: CGRect(x:0, y:0, width:width, height:height))
        carouselView.center = CGPoint(x:width / 2,y: height / 2)
        self.view.addSubview(carouselView)
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        carouselView.scrollToFirstItem()
    }

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


}