title: Rebuild stateful widget on update of other stateful widget in Flutter
body: <p>I have two stateful widgets. 
  One I'll call the parent, because it's producing a list (of map markers) that is being passed to the second widget (the child, a map, in a different dart file).
  I have a default list of markers that is updated in an async function in the parent widget.
  Despite using setState() to update the list, the child widget (map) is unaffected by this update. 
  Is there any way I can await before passing data to a widget in the build method?</p>
  
  <pre><code>
  class ParentWidget extends StatefulWidget{
          .............
  }
  
  class _ParentWidgetState extends State&lt;ParentWidget&gt; {
  
  List markers = [LatLng(0,0)];
  
  @override
    void initState() {
      super.initState();
      updateMarkers();
  }
  
  updateMarkers () async {
    updatedMarkers = await getUpdatedMarkers()
    setState((){
      markers = updatedMarkers
    });
    # # print(updatedMarkers)
    # # ^^ prints the correct data that I want to pass in MyMap
  }
  
  @override
    Widget build(BuildContext context) {
    return Scaffold(
    ............
    body: MyMap(markers: markers);
   # # The original markers ([LatLng(0,0)]) is the only data getting passed to MyMap
   # # How can I get the updatedMarkers passed to the MyMap widget???????
  }
  </code></pre>