title: UIKeyboardWillShowNotification calling twice ios 9
body: <p>I am using <code>UIKeyboardWillShowNotification</code>to detect when a textfield is selecting by user and the keyboard is opening. In ios 8 and older versions of iOS it is working fine but today I upgrade to iOS 9 and xCode 7. the problem is that in iOS now the notification is called after selecting each textfields (while in ios 8 only called after selecting first textfield).</p>
  
  <p>I searched about this and find some post like <a href="https://stackoverflow.com/questions/22549911/why-is-uikeyboardwillshownotification-called-every-time-new-textfield-is-selecte">Why is UIKeyboardWillShowNotification called every time another TextField is selected?</a></p>
  
  <p>but it is not about iOS 9 (actually every thing was right in iOS8 and by upgrading I see the problem) and I am not using inputAccessoryViews too.</p>