title: iOS - UITableView refresh table properly?
body: <p>I have lots of data and lots of rows in my tableView.
  when data changes I want to update my visible cells on the screen, I really don't want to use reloadData because it's an expensive call.</p>
  
  <p>Is it possible to somehow update the visible cells only?
  I tried calling : <code>beginUpdate</code> &amp; <code>endUpdate</code> on the table, but that doesn't work all the time?</p>
  
  <p>Any suggestions?</p>