title: Attempt to present UIViewController while a presentation is in progress!-Warning
body: <p>Assume a new iOS project, just with a navigation controller (correctly wired as entry point) and an overridden viewDidAppear() containing the following three lines of code:</p>
  
  <pre><code>            self.presentViewController(UIViewController(), animated: true, completion: nil)
              self.dismissViewControllerAnimated(true, completion: {})
              self.presentViewController(UIViewController(), animated: true, completion: nil)
  </code></pre>
  
  <p>When executed, that code will raise a warning "Attempt to present UIViewController while a presentation is in progress!" when attempting to present the second controller.</p>
  
  <p>Question: What exactly am I missing in order to dismiss the controller correctly before calling another controller?</p>