title: how to get index of the element in focus for a horizontal scrollview
body: <p>i have this horizontal scroll view in my code. This horizontalscrollview has a series of imageviews in it. Whenever i swipe my finger and the scroll moves from one image to another, i need to find the index of the view now in focus.
  In short i need some way to identify which child element of the horizontalscrollview is in focus right now so that i can do stuff based on that.</p>
  
  <p>thank you in advance.</p>