title: UICollectionView: UICollectionViewCell object is always null in sizeForItemAtIndexPath
body: <p>I have a collection view that contains different custom cells.</p>
  
  <p>These cells contain different content that varies in size.</p>
  
  <p>The cells are defined in the Storyboard, so no registering needed in code.</p>
  
  <p>All i want to do now is change the size in the delegate method depending on the content:</p>
  
  <pre><code>- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
  
  id cellAtIndexPath = [collectionView cellForItemAtIndexPath:indexPath];
  
  NSLog(@"The cell: %@", cellAtIndexPath);
  
  ...
  e.g. calling sizeToFit methods and cumulating the sizes of the cells' subviews
  ...
  
  }
  </code></pre>
  
  <p>The Method is called as expected for every cell, but cellAtIndexPath always returns NULL, no matter what i tried.
  So i am not able to access the cell object at the indexPath or its content view.</p>
  
  <p>Any suggestions why i cannot access the cell object?</p>