title: Flatlist scroll position onScroll
body: <p>I am building a header that animates/hides as the user scrolls down a Flatlist.
  Is there any way to find out the scroll position of the Flatlist in pixels?</p>
  
  <p>I'm using react native 0.59.8.
  I've tried using onScroll hoping it passes a value to the callback - it doesn't.
  I've also tried onScrollBeginDrag, onScrollEndDrag and onMomentumScrollEnd.. None of them provide information of the current scroll position.</p>
  
  <pre><code>onSroll={(info)=&gt;{console.log(info)}
  </code></pre>
  
  <p>I would expect to get some information about the scroll, but none is passed.</p>