Flutter Service Architecture

0_main.dart

import 'package:architecture_playground/home_page.dart';
import 'package:architecture_playground/services.dart';
import 'package:flutter/material.dart';

void main() async {
  // perform long-running tasks before "runApp" to display the native splash screen
  final services = await Services.initialize();

  runApp(ServicesProvider(
    services: services,
    child: App(),
  ));
}

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Architecture Demo',
      home: HomePage(),
    );
  }
}

1_services.dart

import 'package:flutter/widgets.dart';
import 'package:rxdart/rxdart.dart';
import 'package:shared_preferences/shared_preferences.dart';

/// Service container
class Services {
  final SharedPreferences sharedPrefs;
  final DataService dataService;
  final AuthService authService;

  Services(this.sharedPrefs, this.dataService, this.authService);

  static Future<Services> initialize() async {
    final sharedPrefs = await SharedPreferences.getInstance();

    final dataService = DataService();
    await dataService.initialize();

    // service that depends on other services
    final authService = AuthService(sharedPrefs, dataService);

    return Services(sharedPrefs, dataService, authService);
  }

  static Services of(BuildContext context) {
    // A bit different from a normal inherited widget. Widgets can call this from initState,
    // and it is assumed that the services never change during the lifetime of the app
    final provider = context.ancestorInheritedElementForWidgetOfExactType(ServicesProvider).widget as ServicesProvider;
    return provider.services;
  }
}

class ServicesProvider extends InheritedWidget {
  final Services services;

  ServicesProvider({Key key, this.services, Widget child}) : super(key: key, child: child);

  @override
  bool updateShouldNotify(ServicesProvider old) {
    if (services != old.services) {
      throw Exception('Services must be constant!');
    }
    return false;
  }
}

// Example services:

class AuthService {
  final SharedPreferences _sharedPrefs;
  final DataService _dataService;

  AuthService(this._sharedPrefs, this._dataService);

// getters, fields, methods, obervables...
}

class DataService {
  Observable<int> get magicNumber$ => _magicNumber$;
  final _magicNumber$ = BehaviorSubject<int>();

  DataService() {}

  Future<void> initialize() async {
    // open database, contact server...
    await Future.delayed(Duration(seconds: 2));

    _magicNumber$.add(42);
  }

  void increaseMagic() {
    _magicNumber$.add(_magicNumber$.value + 1);
  }
}

2_home_page.dart

import 'package:architecture_playground/home_bloc.dart';
import 'package:architecture_playground/services.dart';
import 'package:flutter/material.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  HomeBloc _bloc;

  @override
  void initState() {
    super.initState();
    // "HomeBloc" is a scoped service. There's no DI, so we have to initialize it manually.
    // if required, you can create another provider InheritedWidget to make it available to child widgets
    final services = Services.of(context);
    _bloc = HomeBloc(services.dataService);
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Architecture Demo')),
      body: StreamBuilder<String>(
        stream: _bloc.magicString$,
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            return Center(
              child: Text(snapshot.data),
            );
          } else {
            return Loading();
          }
        },
      ),
    );
  }
}

class Loading extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: CircularProgressIndicator(),
    );
  }
}

3_home_bloc.dart

import 'package:architecture_playground/services.dart';
import 'package:rxdart/rxdart.dart';

class HomeBloc {
  final DataService _dataService;

  Observable<String> get magicString$ => _magicString$;
  Observable<String> _magicString$;

  HomeBloc(this._dataService) {
    _magicString$ = _dataService.magicNumber$.map((n) => 'The magic number is $n');
  }

  void dispose() {
    // do stuff when UI model is disposed
  }
}

4_pubspec.yaml

name: architecture_playground
description: A new Flutter application.

version: 1.0.0+1

environment:
  sdk: ">=2.0.0-dev.68.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^0.1.2
  shared_preferences: ^0.4.3
  rxdart: ^0.19.0

dev_dependencies:
  flutter_test:
    sdk: flutter

flutter:
  uses-material-design: true