title: Observe keyboard notifications *only* from UITextView? Passing UITextView to "object" parameter isn't working
body: <p>Assume a view controller contains both a UITextView and a UITextField. If the goal is to observe keyboard notifications from <em>only</em> the UITextView, shouldn't the following code work?</p>
  
  <p>Unfortunately, it doesn't work. The function associated with the notification never gets invoked. Is there a way to observe keyboard notifications only from the UITextView?</p>
  
  <p>The reason it matters is because we need to scroll the parent UIView for the UITextView and not for the UITextField. Otherwise, the keyboard obscures the UITextView.</p>
  
  <pre><code>class CustomViewController: UIViewController {
  
      @IBOutlet weak var promptField: UITextView!
      @IBOutlet weak var nameField: UITextField!
  
      override func viewDidLoad() {
          super.viewDidLoad()
  
          // Get notified when keyboard appears
          NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillShow:", name: UIKeyboardWillShowNotification, object: promptField)
      }
  
      func keyboardWillShow(notification: NSNotification) {
          // Do stuff
      }
  }
  </code></pre>