class ProgressModel extends InheritedStream<ValueStream<double>> {
  const ProgressModel({
    Key key,
    ValueStream<double> stream,
    Widget child,
  }) : super(key: key, stream: stream, child: child);

  static double of(BuildContext context) {
    return context
        .dependOnInheritedWidgetOfExactType<ProgressModel>()
        .stream
        .value;
  }
}

class _MyState extends State<MyPage> {
  final _subject = BehaviorSubject<double>.seeded(0.0);

  @override
  void dispose() {
    _subject.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ProgressModel(
        stream: _subject.stream,
        child: Progress(),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => _subject.add(Random.nextDouble()),
      ),
    );
  }
}

class Progress extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return CircularProgressIndicator(value: ProgressModel.of(context));
  }
}