title: collectionview trying to call cellForItem in viewDidLoad exception
body: <p>I'm trying to select some cells by traversing them and checking the text of a button. I tried checking the count of my collection view and it shows 5 before getting an exception force casting the cell.</p>
  
  <p>Here's my code:</p>
  
  <pre><code>for index in 0..&lt;array.count {
        let indexPath = IndexPath(item: index, section: 0)
  
        let cell = ingestionCollectionView.cellForItem(at: indexPath) as! cvcBase
  
         //Set property of the cell              
  }
  </code></pre>
  
  <p>When I call this exact code in the viewWillAppear I get the same exception.. when I call it in viewDidAppear I don't get an exception but I can notice a delay in the action I'm performing.</p>
  
  <p>The code crashes on this line <code>let cell = ingestionCollectionView.cellForItem(at: indexPath) as! cvcBase</code> and if I don't force downcast then the <code>UICollectionViewCell</code> is nil.</p>
  
  <p>Error message: </p>
  
  <pre><code>fatal error: unexpectedly found nil while unwrapping an Optional value
  2017-02-20 19:43:30.093023 Project[1073:218460] fatal error: unexpectedly found nil while unwrapping an Optional value
  </code></pre>