title: Determine when unwind segue animation is completed
body: <p>I have a custom dismiss animation that uses <code>UIPercentDrivenInteractiveTransition</code> and <code>UIViewControllerAnimatedTransitioning</code>. It is initiated by an unwind segue and the transitioning delegate is set up in <code>prepareForSegue:</code>.</p>
  
  <p>In my presenting view controller, the unwind IBAction keeps getting called as soon as I begin the segue, instead of when the segue is completed. This is problematic since my dismiss animation is gesture driven, so we do not know how long it will take to complete.</p>
  
  <p>Is there a way to know when the segue has completed its animation?</p>
  
  <p>Neither <code>viewWillAppear:</code> nor <code>viewDidAppear:</code> seem to get called at the moment of completion, I assume this is because the segue is an unwind segue.</p>