title: Flutter ScrollController position in NestedScrollView
body: <p>I have a <code>NestedScrollView</code> that houses a <code>SliverAppBar</code> with a <code>TabBarView</code> and the tabs consist of an infinite loading list each. Right now I only have one <code>ScrollController</code> attached to <code>NestedScrollView</code>, and list widgets read the scroll position of this controller.</p>
  
  <p>The infinite loading logic uses <code>controller.position.extentAfter</code> to decide when to fetch data from the API. But with multiple tabs, I get the error </p>
  
  <p><strong>ScrollController attached to multiple scroll views.</strong></p>
  
  <p>I tried reading about <code>controller.positions</code> but couldn't make sense of the 2 line documentation that's available. My question is, is it possible to access scroll positions per page in a <code>TabBarView</code> or should I just use separate <code>ScrollController</code> for each of those and forget about the correct scrolling of slivers?</p>