title: How to prevent an iPhone app from closing until all activity is done
body: <p>My app communicates wirelessly to an external device.  I want to prevent the user from closing the app until a response is received from the device, which can take a few seconds.</p>
  
  <p>In the ViewController.viewWillDisappear and also the appDelegate.applicationWillTerminate I can put logic to see if there is still something left to do, but I can't determine how to keep the app from closing anyway!</p>
  
  <p>I recognize that the 'performance' of the phone will look bad if the app doesn't close quickly, but I would put up a view explaining to the user that the app must complete before shutting down AND be patient.</p>
  
  <p>Anyone know of a way to do this?</p>