Recipe: Bloc Access (Generated Routes)

main.dart

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

class SimpleBlocDelegate extends BlocDelegate {
  @override
  void onEvent(Bloc bloc, Object event) {
    super.onEvent(bloc, event);
    print(event);
  }

  @override
  void onTransition(Bloc bloc, Transition transition) {
    super.onTransition(bloc, transition);
    print(transition);
  }

  @override
  void onError(Bloc bloc, Object error, StackTrace stacktrace) {
    super.onError(bloc, error, stacktrace);
    print(error);
  }
}

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

class AppRouter {
  final _counterBloc = CounterBloc();

  Route onGenerateRoute(RouteSettings settings) {
    switch (settings.name) {
      case '/':
        return MaterialPageRoute(
          builder: (_) => BlocProvider.value(
            value: _counterBloc,
            child: HomePage(),
          ),
        );
      case '/counter':
        return MaterialPageRoute(
          builder: (_) => BlocProvider.value(
            value: _counterBloc,
            child: CounterPage(),
          ),
        );
      default:
        return null;
    }
  }

  void dispose() {
    _counterBloc.close();
  }
}

class App extends StatefulWidget {
  @override
  _AppState createState() => _AppState();
}

class _AppState extends State<App> {
  final _router = AppRouter();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      onGenerateRoute: _router.onGenerateRoute,
    );
  }

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

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counterBloc = BlocProvider.of<CounterBloc>(context);
    return Scaffold(
      appBar: AppBar(title: Text('Counter')),
      body: Center(
        child: RaisedButton(
          onPressed: () => Navigator.of(context).pushNamed('/counter'),
          child: Text('Counter'),
        ),
      ),
      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.add(CounterEvent.increment);
              },
            ),
          ),
          Padding(
            padding: EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              heroTag: 1,
              child: Icon(Icons.remove),
              onPressed: () {
                counterBloc.add(CounterEvent.decrement);
              },
            ),
          ),
        ],
      ),
    );
  }
}

class CounterPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Counter'),
      ),
      body: BlocBuilder<CounterBloc, int>(
        builder: (context, count) {
          return Center(
            child: Text('$count'),
          );
        },
      ),
    );
  }
}

enum CounterEvent { increment, decrement }

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

  @override
  Stream<int> mapEventToState(CounterEvent event) async* {
    switch (event) {
      case CounterEvent.decrement:
        yield state - 1;
        break;
      case CounterEvent.increment:
        yield state + 1;
        break;
    }
  }
}

updated code for flutter_bloc 8.1.3

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

@immutable
class SimpleBlocObserver extends BlocObserver {
  @override
  void onEvent(Bloc bloc, Object? event) {
    super.onEvent(bloc, event);
    // ignore: avoid_print
    print(event ?? 'event was null');
  }

  @override
  void onTransition(Bloc bloc, Transition transition) {
    super.onTransition(bloc, transition);
    // ignore: avoid_print
    print(transition);
  }

  @override
  void onError(BlocBase bloc, Object error, StackTrace stackTrace) {
    super.onError(bloc, error, stackTrace);
    // ignore: avoid_print
    print(error);
  }
}

void main() {
  Bloc.observer = SimpleBlocObserver();
  runApp(const App());
}

class AppRouter {
  static Route<dynamic> _errorRoute() {
    return MaterialPageRoute(builder: (context) {
      return Scaffold(
          appBar: AppBar(
            title: const Text('Error Route'),
            centerTitle: true,
          ),
          body: const Center(
            child: Text('Page not found!'),
          ));
    });
  }

  final _counterBloc = CounterBloc();

  Route onGenerateRoute(RouteSettings settings) {
    switch (settings.name) {
      case '/':
        return MaterialPageRoute(
          builder: (_) => BlocProvider.value(
            value: _counterBloc,
            child: const HomePage(),
          ),
        );
      case '/counter':
        return MaterialPageRoute(
          builder: (_) => BlocProvider.value(
            value: _counterBloc,
            child: const CounterPage(),
          ),
        );
      default:
        return _errorRoute();
    }
  }

  void dispose() {
    _counterBloc.close();
  }
}

class App extends StatefulWidget {
  const App({super.key});

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  final _router = AppRouter();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      onGenerateRoute: _router.onGenerateRoute,
    );
  }

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

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    final counterBloc = BlocProvider.of<CounterBloc>(context);
    return Scaffold(
      appBar: AppBar(title: const Text('Counter')),
      body: Center(
        child: ElevatedButton(
          onPressed: () => Navigator.of(context).pushNamed('/counter'),
          child: const Text('Counter'),
        ),
      ),
      floatingActionButton: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          Padding(
            padding: const EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              heroTag: 0,
              child: const Icon(Icons.add),
              onPressed: () {
                counterBloc.add(Increment());
              },
            ),
          ),
          Padding(
            padding: const EdgeInsets.symmetric(vertical: 5.0),
            child: FloatingActionButton(
              heroTag: 1,
              child: const Icon(Icons.remove),
              onPressed: () {
                counterBloc.add(Decrement());
              },
            ),
          ),
        ],
      ),
    );
  }
}

class CounterPage extends StatelessWidget {
  const CounterPage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Counter'),
      ),
      body: BlocBuilder<CounterBloc, int>(
        builder: (context, count) {
          return Center(
            child: Text('$count'),
          );
        },
      ),
    );
  }
}

@immutable
sealed class CounterEvent {}

final class Increment extends CounterEvent {}

final class Decrement extends CounterEvent {}

class CounterBloc extends Bloc<CounterEvent, int> {
  CounterBloc() : super(0) {
    on<Increment>((event, emit) => emit(state + 1));
    on<Decrement>((event, emit) => emit(state - 1));
  }
}