CircularQueue+UICollectionView

CircularQueuePlayground.swift

import UIKit
import PlaygroundSupport

class CircularQueue<T> : IteratorProtocol, RandomAccessCollection {
    typealias Element = T
    public typealias Index = Int
    public typealias Indices = CountableRange<Int>
    
    var position = 0
    let items : [T]
    
    init(items:[T]){
        self.items = items
    }
    
    func next() -> T? {
      let item = items[position]
      position = ((position + 1) % items.count)
      return item
    }
    
    public var startIndex: Int {
        return 0
    }
    
    public var endIndex: Int {
        return items.count
    }
    
    public func index(after i: Int) -> Int {
        _precondition(i == startIndex)
        return endIndex
    }
    
    public func index(before i: Int) -> Int {
        _precondition(i == endIndex)
        return startIndex
    }
    
    public subscript(position: Int) -> Element {
        get {
            let pos = (position % items.count)
            return items[pos]
        }
        set {
            
        }
    }
}

class CollectionViewController : UICollectionViewController {
    
    let arrColor : [UIColor] = [.green,.yellow,.blue,.purple,.orange]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.collectionView?.backgroundColor = .white
        self.collectionView?.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "PlayCell")
    }
    
    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 10000
    }
    
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "PlayCell", for: indexPath)
        let queue = CircularQueue(items: arrColor)
        cell.backgroundColor = queue[indexPath.row]
        return cell
    }
    
}

PlaygroundPage.current.liveView = CollectionViewController(collectionViewLayout: UICollectionViewFlowLayout())