title: scrollViewDidScroll is not getting called
body: <p>I have a custom tab bar with a horizontal scroll view underneath that. 
  Tab bar contains 5 buttons each of them calls one of the five custom keyboards (they are placed on a scroll view). You can switch between these keyboards scrolling the scroll view or pressing the buttons. </p>
  
  <p>Question: how do I change the states of the buttons (default &lt;-> selected) when I switch between keyboards using scroll view? </p>
  
  <p><em>Visual:</em></p>
  
  <p><a href="https://i.stack.imgur.com/Kks3L.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Kks3L.png" alt="enter image description here"></a></p>