title: I can't connect the IBAction of UIButton into the ViewController class
body: <p>When I try to link the <code>UIButton</code> object to the <code>ViewController</code> class in order the create an <code>IBAction</code>, Xcode doesn't show me the window for creating it. 
  I have to say that It only happens with the second <code>ViewController</code> of the <code>NavigationController</code>, because with the first one it works. 
  I believe it should be a Xcode bug...
  The situation is the one below: </p>
  
  <p><a href="https://i.stack.imgur.com/MnfDz.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MnfDz.jpg" alt="enter image description here"></a></p>