[flutter_bloc] Location Stream Example

main.dart

import 'dart:async';

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: BlocProvider<LocationBloc>(
        create: (context) =>
            LocationBloc(geolocator: Geolocator())..add(LocationStarted()),
        child: Home(),
      ),
    );
  }
}

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Home')),
      body: BlocBuilder<LocationBloc, LocationState>(
        builder: (context, state) {
          if (state is LocationInitial) {
            return Center(child: Text('Fetching Location'));
          }
          if (state is LocationLoadSuccess) {
            return Center(
              child: Text(
                'Location: (${state.position.latitude}, ${state.position.longitude})',
              ),
            );
          }
          return Center(child: CircularProgressIndicator());
        },
      ),
    );
  }
}

@immutable
abstract class LocationEvent {}

class LocationStarted extends LocationEvent {}

class LocationChanged extends LocationEvent {
  final Position position;

  LocationChanged({@required this.position});
}

@immutable
abstract class LocationState {}

class LocationInitial extends LocationState {}

class LocationLoadInProgress extends LocationState {}

class LocationLoadSuccess extends LocationState {
  final Position position;

  LocationLoadSuccess({@required this.position});
}

class LocationBloc extends Bloc<LocationEvent, LocationState> {
  final Geolocator _geolocator;
  StreamSubscription _locationSubscription;

  LocationBloc({@required Geolocator geolocator})
      : assert(geolocator != null),
        _geolocator = geolocator;

  @override
  LocationState get initialState => LocationInitial();

  @override
  Stream<LocationState> mapEventToState(
    LocationEvent event,
  ) async* {
    if (event is LocationStarted) {
      yield LocationLoadInProgress();
      _locationSubscription?.cancel();
      _locationSubscription = _geolocator.getPositionStream().listen(
            (Position position) => add(
              LocationChanged(position: position),
            ),
          );
    } else if (event is LocationChanged) {
      yield LocationLoadSuccess(position: event.position);
    }
  }

  @override
  Future<void> close() {
    _locationSubscription?.cancel();
    return super.close();
  }
}

pubspec.yaml

name: example
description: A new Flutter project.

version: 1.0.0+1

environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  bloc: ^2.0.0
  equatable: ^1.0.0
  flutter_bloc: ^2.1.0
  geolocator: ^5.1.5

flutter:
  uses-material-design: true