title: How to handle back button using view pager?
body: <p>I am having two fragments Frag A and Frag B which are rendered using view pager . 
  If user has swiped  from A to B then presses back button(when in B) then user should go to A instead of coming out of view pager . How can we achieve this ?</p>
  
  <p>Adding transaction to backstack does not seem to help . </p>
  
  <p>Thanks</p>