title: Buttons scrolling the gallery
body: <p>In my application I have a <code>Gallery</code> view and two buttons to scroll it - left and right. Scrolling the gallery by fling also works, and here is the problem: how can I update the states of buttons after the user scrolled the <code>Gallery</code> using fling movements? Is there any callback that tells that <code>Gallery</code>'s selected item has changed? Thanks. </p>