title: Animate the changing of data in a collectionView
body: <p>I'd like to animate a change in my UICollectionView. I have the collectionView as an <code>@IBOutlet</code>:</p>
  
  <pre><code>@IBOutlet weak var collectionView: UICollectionView!
  </code></pre>
  
  <p>And the collection view reloads (so I can change the alpha of each cell) like this:</p>
  
  <pre><code>var bulkAwardMode = false;
  
  @IBAction func bulkAwardToggleClicked(sender: UIButton) {
      if(bulkAwardMode == false) {
          bulkAwardMode = true
      } else {
          bulkAwardMode = false
      }
      dispatch_async(dispatch_get_main_queue(), {
          self.collectionView.reloadData()
      })
  }
  </code></pre>
  
  <p>However as this is not animated, I tried changing the <code>reloadData()</code> line to  <code>self.collectionView.reloadSections(NSIndexSet(index: 0))</code>, however this just causes a crash with the error <code>attempt to create view animation for nil view</code>.</p>
  
  <p>I'm clearly doing something wrong, but I'm not quite sure what. I did also try putting the code in a <code>UIView.animateWithDuration</code> block, but that also failed.</p>