title: UIBarButtonItem on UINavigationBar in UITabBarController
body: <p>I'm new here. Sorry for may English.</p>
  
  <p>I work on an iPhone application, which has an Tab Bar Controller (within an Navigation Controller). The Tab Bar Controller has four tabs and an Navigation Bar with default Back Button. I will set an other Bar Button Item on this Navigation Bar (on Tab Bar Controller). That is easy with drag and drop on storyboard, but I can't set an action for this new bar button item. </p>
  
  <p>I know that I should set up a delegate for my UITabBarController, but I don't know how.
  Can anyone help?</p>
  
  <p>Thanks!</p>