title: How to determine the scroll direction of ListView
body: <p>I have spent whole day to figure out the direction of scroll of <code>ListView</code> but could not find any solution.
  What I want to achieve is movable header of ListView like "Google Now" search, which goes up while scrolling down and comes back as soon as you scroll up.</p>
  
  <p>What I already have tried so far:</p>
  
  <p>Implemented custom ListView overrode <code>onScrollChanged</code> but it always gives 0 for all attributes.</p>
  
  <p>Can anyone put me on the right track.</p>
  
  <p><img src="https://i.stack.imgur.com/qzO6V.png" alt="enter image description here"></p>