title: iOS: Checking for remote file updates
body: <p>I have a few UITableViews that gather their content from remote XML files.  Sometimes the file is updated, but the view is not updated, because I load the file in my viewDidLoad method.</p>
  
  <p>I am assuming I should do a check in viewDidAppear and load my XML file again.  But I don't want it loading every time the user clicks back to that view.</p>
  
  <p>What is the best way to do this?  Can I somehow check the updated date of a remote file on the web?  Or should I store the updated date in my app, then check at an interval?  There must be a preferred way to do this, so that I know that the XML file has been updated.</p>
  
  <p>Thanks.</p>