title: UITableView delegate method called twice
body: <p>Today my question is about UITableViewController-s
  In particular I have noticed that the datasource delegate method </p>
  
  <pre><code>- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView;
  </code></pre>
  
  <p>is called twice (even if for instance I just create a navigation based application and without adding a line of code.. well adding an NSLog to track it).
  Now, since in my application I need to determine the number of sections basing the choice on the documents in the file system, I need to call some methods to do so. I have put these methods in the above mentioned method, so they will be called twice, which is something I don't need.
  The questions are why is it called twice, can I have it called once?
  I hope that in the official documentation this is not clearly stated (which would mean that I didn't read it at all :) ). By the way I could see others posting similar questions, but I couldn't find a fully satisfying answer.
  Thank you.</p>