title: UIScrollView scroll by offset
body: <p>I've this situation:</p>
  
  <ul>
  <li>one scrollView that fit all screen</li>
  <li>N "cells" inside scrollView, each of them contains a label</li>
  <li>each cell is 80px on height</li>
  <li>fixed green mask (UIView)</li>
  </ul>
  
  <p>I programmatically create the cells (UIView) with label inside and correctly set contentSize of scrollView.</p>
  
  <p>I know that </p>
  
  <pre><code>scrollView.setContentOffset(CGPoint(x: 0, y: 80.0), animated: true)
  </code></pre>
  
  <p>move scroll view by 80.</p>
  
  <p>How can I "override" scroll view behaviour in order to always scroll by 80? 
  What i want is sort of picker behaviour.. is this possible?</p>
  
  <p><img src="https://i.stack.imgur.com/scuQv.png" alt="enter image description here"></p>