 import StoreKit
 
 
-class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, SKProductsRequestDelegate {
+class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, SKProductsRequestDelegate, SKPaymentTransactionObserver {
 
     @IBOutlet weak var collectionView: UICollectionView!
     

    }
    
    
    // MARK: Core Data Function
    
    func createArt(title: String, imageName: String, productIdentifier: String, purchased: Bool) {

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.gallery.count
    }
    
    
    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier("ArtCollectionViewCell", forIndexPath: indexPath) as! ArtCollectionViewCell
