title: iOS - NSNotificationCenter multiple UIKeyboard notification
body: <p>I have two view controllers let's call them A and B</p>
  
  <p>(1) in A I show a popOver containing a textField<br>
  (2) in B there is an UITextView used for simple text editing  </p>
  
  <p>I Have to manage the keyboard in A and in B to scroll the content hidden by the keyboard. I know how to reposition the content. What I need is a way to have different behavior on the same notifications types that in my are UIKeyboardWill(Show/Hide)Notification.<br>
  What I've done so far :<br>
  (1) I've added this code in each controller<br>
  <pre><code>
      [[NSNotificationCenter defaultCenter] addObserver:self
                                    selector:@selector(keyboardDidAppear:)
                                        name:UIKeyboardWillShowNotification
                                      object:self.view.window
  </pre></code>
  as I said I've added this code to A and B, but doesn't work as I expected. For instance
  When I click inside the textView two methods are triggered the keyboardDidAppear of A and the keyboardDidAppear of B, the same happens with the UIKeyboardWillHideNotification.
  I'm sure I'm doing something wrong, but honestly I can't figure it out.  </p>