title: Why does UICollectionView log an error when the cells are fullscreen?
body: <p>I have a <code>UICollectionViewController</code> using a <code>UICollectionViewFlowLayout</code> where my <code>itemSize</code> is the size of the <code>UICollectionView</code>. Basically, this is a line layout of cells where each cell is fullscreen and scrolls horizontally. </p>
  
  <p>In my <code>UICollectionViewFlowLayout</code> subclass, I have overridden <code>prepareLayout</code> as follows:</p>
  
  <pre><code>- (void)prepareLayout {
      self.itemSize = self.collectionView.frame.size;
      self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
      self.collectionView.pagingEnabled = YES;
      self.minimumLineSpacing = 0.0;
      self.minimumInteritemSpacing = 0.0;
      self.sectionInset = UIEdgeInsetsZero;
      self.footerReferenceSize = CGSizeZero;
      self.headerReferenceSize = CGSizeZero;
  }
  </code></pre>
  
  <p>The <code>UICollectionViewController</code> is very basic returning 10 items in one section. I've included a <a href="https://github.com/w5mith/FullScreenCollectionViewLineLayoutErrorExample">sample project on GitHub</a> for more detail. </p>
  
  <p>Everything appears to be set up correctly. It looks right in the simulator and on the device but, when the collection view is displayed, there is an error logged to the console:</p>
  
  <blockquote>
  <pre><code>the behavior of the UICollectionViewFlowLayout is not defined because:
  the item height must be less that the height of the UICollectionView minus the section insets top and bottom values.
  </code></pre>
  </blockquote>
  
  <p><em>Note also that the collection view controller in my example is in a navigation controller and while that doesn't look particularly necessary in the example, in my real-world case I need the collection view in a navigation controller.</em></p>