gistfile1.txt

//: Playground - noun: a place where people can play

import UIKit
import XCPlayground

var str = "Hello, playground"
private let reuseIdentifier = "Cell"
class NumberCell: UICollectionViewCell {
    let numberLabel = UILabel()
    
    override var selected: Bool {
        didSet {
            // Updates as expected
            contentView.backgroundColor = self.selected ? UIColor.redColor() : UIColor.clearColor()
        }
    }
    
    var number: Int? {
        didSet {
            // Sets and shows the text in the number label as expected when cell is first initialised
            if let number = number {
                numberLabel.text = String(number)
            }
        }
    }
    
    var isCrossedOut: Bool = false {
        didSet {
            // Sets and displays correct values on initialisation, but later
            // stops updating display
            contentView.backgroundColor = self.isCrossedOut ? UIColor.blackColor() : UIColor.clearColor()
        }
    }
    
    // ...
}
class CollectionViewController: UICollectionViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Uncomment the following line to preserve selection between presentations
        // self.clearsSelectionOnViewWillAppear = false
        
        // Register cell classes
        collectionView!.registerClass(NumberCell.self, forCellWithReuseIdentifier: "Cell")

        // Do any additional setup after loading the view.
    }
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    /*
    // MARK: - Navigation
    
    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
    }
    */
    
    // MARK: UICollectionViewDataSource
    
    override func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        // #warning Incomplete implementation, return the number of sections
        return 1
    }
    
    
    override func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        // #warning Incomplete implementation, return the number of items
        return 2
    }
    
    override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! NumberCell
        cell.backgroundColor = UIColor.whiteColor()
        // Configure the cell
        
        return cell
    }
    
    // MARK: UICollectionViewDelegate
    
    /*
    // Uncomment this method to specify if the specified item should be highlighted during tracking
    override func collectionView(collectionView: UICollectionView, shouldHighlightItemAtIndexPath indexPath: NSIndexPath) -> Bool {
    return true
    }
    */
    
    /*
    // Uncomment this method to specify if the specified item should be selected
    override func collectionView(collectionView: UICollectionView, shouldSelectItemAtIndexPath indexPath: NSIndexPath) -> Bool {
    return true
    }
    */
    
    /*
    // Uncomment these methods to specify if an action menu should be displayed for the specified item, and react to actions performed on the item
    override func collectionView(collectionView: UICollectionView, shouldShowMenuForItemAtIndexPath indexPath: NSIndexPath) -> Bool {
    return false
    }
    
    override func collectionView(collectionView: UICollectionView, canPerformAction action: Selector, forItemAtIndexPath indexPath: NSIndexPath, withSender sender: AnyObject?) -> Bool {
    return false
    }
    
    override func collectionView(collectionView: UICollectionView, performAction action: Selector, forItemAtIndexPath indexPath: NSIndexPath, withSender sender: AnyObject?) {
    
    }
    */
    override func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
        
    }
    @IBAction func crossOut(sender: AnyObject) {
        let cell = self.collectionView?.cellForItemAtIndexPath(NSIndexPath(forItem: 0, inSection: 0)) as! NumberCell
        cell.isCrossedOut = !cell.isCrossedOut
        //cell.setNeedsDisplay()
    }
    
}

let collectionViewController = CollectionViewController(collectionViewLayout: UICollectionViewFlowLayout())
XCPlaygroundPage.currentPage.liveView = collectionViewController.collectionView
collectionViewController.crossOut(collectionViewController)