title: Detecting that back was pressed to get to current view controller
body: <p>I am using the navigation controller to go back from one view to previous view using the code below.</p>
  
  <p>ChildViewController.swift:</p>
  
  <pre><code>self.navigationController.popViewControllerAnimated(true)
  </code></pre>
  
  <p>I need a way to detect that the navigation controller went to the previous view in the actual previous view like below.</p>
  
  <p>ParentViewController.swift:</p>
  
  <pre><code>func backWasPressed(viewControllerIdentifier: String!) {
      // if back was pressed from this view controller and not from any other view
      if viewControllerIdentifier == "ChildViewController" {
              // do stuff here
      }
  }
  </code></pre>
  
  <p>Is there anyway to do this?</p>