title: How do I pre-calculate cell heights on a background thread to improve table view performance?
body: <p>I've heard of this tactic to improve cell loading performance quite a few times, and it's mentioned as a technique in <a href="http://blog.jaredsinclair.com/post/81410534498/cell-height-caching-dilemmas-in-unread" rel="nofollow">this blog post by Jared Sinclair</a>, but how would I go about doing this?</p>
  
  <p>To my knowledge the table view (if you don't supply an estimated row height) asks for the height of every cell in the table view as soon as it has a data source. Therefore, at what point would I be able to do "pre-calculations"? In my head that would mean supplying a handful at the beginning to allow the table view to have a foundation, then calculate the rest on a background thread. But this doesn't seem possible, as the table view asks for <em>all</em> the cell heights.</p>
  
  <p>In Jared Sinclair's post he also mentions that he does this <em>instead</em> of estimated row height, so I don't think that would have anything to do with the solution.</p>
  
  <p>So how do I leverage background threads to improve cell height loading? From what I can tell my app has a several second delay when about to display around 100 variable-height cells, and I'd like to improve this.</p>