title: UIPanGestureRecognizer does not work
body: <p>It's weird, but when I add a <code>UIPanGestureRecognizer</code> to a view it does not work. It's my view, that white view is a subview of the red view:</p>
  
  <p><a href="https://i.stack.imgur.com/DIxaQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DIxaQ.png" alt="enter image description here"></a></p>
  
  <p><strong>Main View:</strong></p>
  
  <pre><code>@IBOutlet weak var redView: UIView!
  @IBOutlet weak var whiteView: UIView!
  override func viewDidLoad() {
      super.viewDidLoad()
      // Do any additional setup after loading the view, typically from a nib.
      let panRecognizer = UIPanGestureRecognizer(target:self, action:#selector(ViewController.handlePan))
      whiteView.gestureRecognizers = [panRecognizer]        
  }
  
  
  func handlePan(recognizer:UIPanGestureRecognizer)  {
      //foo
  }
  </code></pre>
  
  <p>When I tap and drag the white view it won't move. </p>