title: Reload collection view data when user comes back to view controller
body: <p>Im trying to reload the data every time the view loads but it is not work. code snippet bellow: </p>
  
  <pre><code>override func viewDidLoad() {
      super.viewDidLoad()
      // Register cell classes
      self.collectionView!.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: "cell")
      self.collectionView!.reloadData()
  }
  </code></pre>
  
  <p>but it doesn't work.</p>