Sharing Bloc Across Routes

main.dart

import 'dart:async';

import 'package:flutter/material.dart';

import 'package:bloc/bloc.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

class SimpleBlocDelegate extends BlocDelegate {
  @override
  void onTransition(Transition transition) {
    print(transition.toString());
  }
}

void main() {
  BlocSupervisor().delegate = SimpleBlocDelegate();
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => MyAppState();
}

class MyAppState extends State<MyApp> {
  final CounterBloc _counterBloc = CounterBloc();

  @override
  Widget build(BuildContext context) {
    return BlocProvider<CounterBloc>(
      bloc: _counterBloc,
      child: MaterialApp(
        title: 'Flutter Demo',
        routes: {
          '/': (BuildContext context) => CounterPage(),
          '/otherCounter': (BuildContext context) => OtherCounterPage(),
        },
        initialRoute: '/',
      ),
    );
  }

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

class CounterPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final CounterBloc _counterBloc = BlocProvider.of<CounterBloc>(context);

    return Scaffold(
      appBar: AppBar(
        title: Text('Counter'),
        actions: <Widget>[
          IconButton(
            icon: Icon(Icons.navigate_next),
            onPressed: () {
              Navigator.of(context).pushNamed('/otherCounter');
            },
          )
        ],
      ),
      body: BlocBuilder<CounterEvent, int>(
        bloc: _counterBloc,
        builder: (BuildContext context, int count) {
          return Center(
            child: Text(
              '$count',
              style: TextStyle(fontSize: 24.0),
            ),
          );
        },
      ),
      floatingActionButton: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          Padding(
            padding: EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              heroTag: 0,
              child: Icon(Icons.add),
              onPressed: () {
                _counterBloc.dispatch(Increment());
              },
            ),
          ),
          Padding(
            padding: EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              heroTag: 1,
              child: Icon(Icons.remove),
              onPressed: () {
                _counterBloc.dispatch(Decrement());
              },
            ),
          ),
        ],
      ),
    );
  }
}

class OtherCounterPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final CounterBloc _counterBloc = BlocProvider.of<CounterBloc>(context);

    return Scaffold(
      appBar: AppBar(title: Text('Other Counter Page')),
      body: BlocBuilder<CounterEvent, int>(
        bloc: _counterBloc,
        builder: (BuildContext context, int count) {
          return Center(
            child: Text(
              '$count',
              style: TextStyle(fontSize: 24.0),
            ),
          );
        },
      ),
      floatingActionButton: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          Padding(
            padding: EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              heroTag: 2,
              child: Icon(Icons.add),
              onPressed: () {
                _counterBloc.dispatch(Increment());
              },
            ),
          ),
          Padding(
            padding: EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              heroTag: 3,
              child: Icon(Icons.remove),
              onPressed: () {
                _counterBloc.dispatch(Decrement());
              },
            ),
          ),
        ],
      ),
    );
  }
}

abstract class CounterEvent {}

class Increment extends CounterEvent {
  @override
  String toString() => 'Increment';
}

class Decrement extends CounterEvent {
  @override
  String toString() => 'Decrement';
}

class CounterBloc extends Bloc<CounterEvent, int> {
  @override
  int get initialState => 0;

  @override
  Stream<int> mapEventToState(int currentState, CounterEvent event) async* {
    if (event is Increment) {
      yield currentState + 1;
    }
    if (event is Decrement) {
      yield currentState - 1;
    }
  }
}

@felangel, I haven't had to use this yet, but why is it an issue sharing a bloc across routes?