title: How can I reload only updated cells from UICollectionView
body: <p>I have several cells that are written onto a <code>UICollectionView</code> and reloading them takes a long time. How can I reload only when the data of a cell is modified? Here's one thing I've tried:</p>
  
  <pre><code>  if([oldDataSource count] != [currentDataSource count])
     {
        [collectionView reloadData];
     }
  </code></pre>
  
  <p>Yet, I still don't want to deal with reloading the <em>entire</em> thing. I've also tried:</p>
  
  <pre><code>if([oldDataSource count] &lt; [currentdataSource count])
  {
  //something was added. //reload the last item in the current data source 
  }
  </code></pre>
  
  <p>This also failed because I can't reload something that doesn't "exist" in memory yet. This method also doesn't work because if something was deleted from my data source, the Cell will still remain in the interface, and will crash if clicked on.</p>
  
  <p>So, what's the best way to deal with edited cells?</p>
  
  <p>Thanks!</p>