title: Reload UICollectionView header or footer?
body: <p>I have some data that is fetched in another thread that updates a UICollectionView's header. However, I've not found an efficient way of reloading a supplementary view such as a header or footer. </p>
  
  <p>I can call <code>collectionView reloadSections:</code>, but this reloads the entire section which is unnecessary. <code>collectionView reloadItemsAtIndexPaths:</code> only seems to target cells (not supplementary views). And calling <code>setNeedsDisplay</code> on the header itself doesn't appear to work either. Am I missing something?</p>