Simple Bloc Pattern examples

app.dart

class App extends StatelessWidget {
  final MusicPlayer musicPlayer = DummyMusicPlayer();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: 'Music Player',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: BlocProvider(
          create: (BuildContext context) => MusicPlayerBloc(DummyMusicPlayer()),
          child: MainScreen(),
        ));
  }
}

class MainScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: BlocBuilder<MusicPlayerBloc, MusicPlayerState>(builder: (_, state) {
          if (state is MusicPlayerPlaying) {
            return Text('Playing: ${state.musicTitle}');
          } else if (state is MusicPlayerPaused) {
            return Text('Paused');
          } else {
            return Text('Music Player');
          }
        }),
      ),
      body: Center(
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            BlocBuilder<MusicPlayerBloc, MusicPlayerState>(builder: (context, state) {
              if (state is MusicPlayerIdle || state is MusicPlayerPaused) {
                return SimpleButton(
                    icon: Icons.play_arrow,
                    onPressed: () {
                      BlocProvider.of<MusicPlayerBloc>(context).add(PlayEvent(musicTitle: 'Sandstorm'));
                    });
              } else {
                return SimpleButton(
                    icon: Icons.pause,
                    onPressed: () {
                      BlocProvider.of<MusicPlayerBloc>(context).add(PauseEvent());
                    });
              }
            }),
            BlocBuilder<MusicPlayerBloc, MusicPlayerState>(builder: (_, state) {
              if (state is MusicPlayerPlaying || state is MusicPlayerPaused) {
                return SimpleButton(
                    icon: Icons.stop,
                    onPressed: () {
                      BlocProvider.of<MusicPlayerBloc>(context).add(StopEvent());
                    });
              } else {
                return Container(
                  width: 0,
                );
              }
            })
          ],
        ),
      ),
    );
  }
}

class SimpleButton extends StatelessWidget {
  final Function onPressed;
  final IconData icon;

  SimpleButton({@required this.onPressed, @required this.icon});

  @override
  Widget build(BuildContext context) {
    return IconButton(
      onPressed: onPressed,
      icon: Icon(icon),
      iconSize: 46,
    );
  }
}

app_bar_state_change.dart

AppBar(
        title: BlocBuilder<MusicPlayerBloc, MusicPlayerState>(builder: (_, state) {
          if (state is MusicPlayerPlaying) {
            return Text('Playing: ${state.musicTitle}');
          } else if (state is MusicPlayerPaused) {
            return Text('Paused');
          } else {
            return Text('Music Player');
          }
        }),
      );

bloc_provider_setup.dart

@override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: 'Music Player',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: BlocProvider(
          create: (BuildContext context) => MusicPlayerBloc(DummyMusicPlayer()),
          child: MainScreen(),
        ));
  }

music_player_bloc.dart

class MusicPlayerBloc extends Bloc<MusicPlayerEvent, MusicPlayerState> {
  final MusicPlayer _musicPlayer;

  MusicPlayerBloc(this._musicPlayer) : assert(_musicPlayer != null);

  @override
  MusicPlayerState get initialState => MusicPlayerIdle();

  @override
  Stream<MusicPlayerState> mapEventToState(MusicPlayerEvent event) async* {
    if (event is PlayEvent) {
      final musicTitle = event.musicTitle;
      _musicPlayer.play(musicTitle);
      yield MusicPlayerPlaying(musicTitle: musicTitle);
    } else if (event is PauseEvent) {
      _musicPlayer.pause();
      yield MusicPlayerPaused();
    } else if (event is StopEvent) {
      _musicPlayer.stop();
      yield MusicPlayerIdle();
    }
  }
}

music_player_bloc_empty.dart

class MusicPlayerBloc extends Bloc<MusicPlayerEvent, MusicPlayerState> {

  @override
  MusicPlayerState get initialState => MusicPlayerIdle();

  @override
  Stream<MusicPlayerState> mapEventToState(MusicPlayerEvent event) async* {
    //TODO: Handle Events
  }
}

music_player_event.dart

@immutable
abstract class MusicPlayerEvent {
  const MusicPlayerEvent();
}

class PlayEvent extends MusicPlayerEvent {
  final String musicTitle;
  const PlayEvent({@required this.musicTitle}) : assert(musicTitle != null);
}

class PauseEvent extends MusicPlayerEvent {}

class StopEvent extends MusicPlayerEvent {}

music_player_state.dart

@immutable
abstract class MusicPlayerState {
  const MusicPlayerState();
}

class MusicPlayerIdle extends MusicPlayerState {}

class MusicPlayerPlaying extends MusicPlayerState {
  final String musicTitle;
  const MusicPlayerPlaying({@required this.musicTitle}) : assert(musicTitle != null);
}

class MusicPlayerPaused extends MusicPlayerState {}

play_button.dart

SimpleButton(
  icon: Icons.play_arrow,
  onPressed: () {
      BlocProvider.of<MusicPlayerBloc>(context).add(PlayEvent(musicTitle: 'Sandstorm'));
    });