title: Return to main view controller when app goes in background
body: <p>In my app I have tree view controllers, when the app enters background I want the app to get back to the main view controller. My app is a single application without <code>UINavigationController</code>. </p>
  
  <p>I know that I have to implement this inside:</p>
  
  <pre><code>func applicationWillResignActive(application: UIApplication) {
  
  }
  </code></pre>
  
  <p>but I am not sure how to tell the app to return to the main view controller.</p>
  
  <p>How can I do this?</p>
  
  <p>UPDATE</p>
  
  <p>I have made a small <a href="https://drive.google.com/open?id=0B9zuA_b7fzjJQTJ4d0w3Z3l4TTQ" rel="nofollow">example</a> that takes the app to the main view controllers when enters background. 
  The first Time it goes background the app works fine after I start to get a warning. How can I resolve the warning?  </p>