title: UITabBarController custom action with Storyboard
body: <p>I would like to prompt a user to sign in with a UIAlertView when the user presses a certain tab bar item in a tab bar controller.</p>
  
  <p>This tab bar controller exists in storyboard, and as a result I'm not sure where i can do this. Apple claims that UITabBarController shouldn't be subclassed, further adding to my confusion. And furthermore, i am aware of UITabBarController's delegate pattern but i don't know what view controller i can hook it up to Note: My UITabBarController is generated from a modal segue from a UIViewController.</p>
  
  <p>Thank you in advance.</p>