title: Multi tab / page view in flutter
body: <p>How do i create a multi page view in flutter where the pages correspond to tabs in a bottomnavigationbar such that the widgets corresponding to the pages are built only once and on demand.</p>
  
  <p>For eg., consider a simple facebook app kind of UI with two tabs - the feed and the notification with the following behavior:</p>
  
  <ol>
  <li>Both feed and notifications are list of items fetched over network.</li>
  <li>Assuming the original tab is feed, the notifications should be fetched only when user clicks on the notification tab</li>
  <li>If a user scrolls in the feed, and clicks on notification icon and then clicks again on feed icon, the scroll position should be remembered.</li>
  </ol>
  
  <p>If i use a TabBarView, it rebuilds the widgets every time the tab is changed, so the scroll position is not retained.</p>