collectionViewCell.swift

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! PhotoCollectionViewCell
//        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: PropertyKeys.PhotoCollectionViewCell, for: indexPath) as! PhotoCollectionViewCell
        // Configure the cell
        //直接抓圖庫的圖片
//        cell.photoImageView.image = UIImage(named: "photo\(indexPath.item)")
        //藉由變數photos利用indexPath判斷要顯示哪個item
        cell.photoImageView.image = UIImage(named: "\(photos[indexPath.item])")
        return cell
    }