title: Access Flutter route outside MaterialApp
body: <p>I have a "fixed" custom app bar Widget that sits outside my Material App. I want this app bar to constantly sit at the top and the Widget views to change. </p>
  
  <p>I would like this app bar widget to be able to listen to the routes being updated in the MaterialApp and react accordingly.</p>
  
  <p>I think I need to use a RouteObserver but am struggling to have this app bar subscribe to any route events. I have tried broadcasting a stream to notify any widgets listening to it but this fires from the initState lifecycle hook so only is fired once and not received when calling Navigator.pop()</p>
  
  <p>I have tried this <a href="https://docs.flutter.io/flutter/widgets/RouteObserver-class.html" rel="nofollow noreferrer">https://docs.flutter.io/flutter/widgets/RouteObserver-class.html</a>.</p>
  
  <p>Any ideas on how this can be achieved?</p>