title: Reloading a UICollectionView using reloadData method returns immediately before reloading data
body: <p>I need to know when reloading a UICollectionView has completed in order to configure cells afterwards (because I am not the data source for the cells - other wise would have done it already...)</p>
  
  <p>I've tried code such as </p>
  
  <pre><code>[self.collectionView reloadData];
  [self configure cells]; // BOOM! cells are nil
  </code></pre>
  
  <p>I've also tried using </p>
  
  <pre><code>[self.collectionView performBatchUpdates:^{
    [self.collectionView reloadData];
      } completion:^(BOOL finished) {
          // notify that completed and do the configuration now
    }];
  </code></pre>
  
  <p>but when I reload the data I am getting crashes. </p>
  
  <p>How can I reload the data into the collection, and only when it has finished reloading - do a particular completion handler</p>