Shows how to filter events from a Stream based on events from another Stream

counter_with_deactivate.dart

import 'package:flutter/material.dart';
import 'package:rxdart/rxdart.dart';
import 'package:tuple/tuple.dart';

void main() => runApp(MyApp());

class CounterBloc {
  final _counterSubject = BehaviorSubject.seeded(0);
  final _isActive = BehaviorSubject.seeded(true);
  Stream<int> counter;

  CounterBloc() {
    counter = Observable.combineLatest2(
      _counterSubject,
      _isActive,
      (count, isActive) => Tuple2(count, isActive),
    ).where((tuple) => tuple.item2).map((tuple) => tuple.item1);
  }

  ValueObservable<bool> get active => _isActive;

  void activate() => _isActive.value = true;

  void deactivate() => _isActive.value = false;

  void increment() => _counterSubject.value++;

  void dispose() {
    _counterSubject.close();
    _isActive.close();
  }
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final _bloc = CounterBloc();

  @override
  void dispose() {
    super.dispose();
    _bloc.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            StreamBuilder<int>(
              stream: _bloc.counter,
              builder: (context, snapshot) {
                return Text(
                  '${snapshot.data ?? 0}',
                  style: Theme.of(context).textTheme.display1,
                );
              },
            ),
            StreamBuilder<bool>(
              initialData: _bloc.active.value,
              stream: _bloc.active,
              builder: (context, snapshot) {
                var isActive = snapshot.data;
                return RaisedButton(
                  child: Text(isActive ? 'Deactivate' : 'Activate'),
                  onPressed: () {
                    if (isActive) {
                      _bloc.deactivate();
                    } else {
                      _bloc.activate();
                    }
                  },
                );
              },
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _bloc.increment,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}