Flutter get_it庫，動態服務定位器

• get_it

下面這個demo在兩個頁面都注入了CountService來共享數據

// main.dart
import 'package:get_it/get_it.dart';

GetIt getIt = GetIt.instance;
void main() {
  // 注意注冊順序
  getIt
    ..registerSingleton<LoggerService>(LoggerService())
    ..registerSingleton<CountService>(CountService());
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      initialRoute: '/',
      routes: {
        "/": (c) => HomePage(),
        "/about": (c) => AboutPage(),
      },
    );
  }
}

class HomePage extends StatelessWidget {
  final count = getIt<CountService>(); // 注入

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home Page'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            StreamBuilder(
                stream: count.n$,
                builder: (context, snapshot) {
                  return Text(snapshot.data.toString());
                }),
            FlatButton(
              child: Text('To About'),
              onPressed: () {
                Navigator.of(context).pushNamed('/about');
              },
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: count.add,
      ),
    );
  }
}

class AboutPage extends StatelessWidget {
  final count = getIt<CountService>(); // 注入

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('About Page'),
      ),
      body: Center(
        child: StreamBuilder(
            stream: count.n$,
            builder: (context, snapshot) {
              return Text(snapshot.data.toString());
            }),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: count.add,
      ),
    );
  }
}

class CountService {
  LoggerService loggerService = getIt<LoggerService>();

  Stream<int> get n$ => _nSubject.stream;
  Sink<int> get nSink => _nSubject.sink;
  final _nSubject = BehaviorSubject<int>.seeded(0);
  int _n = 0;

  add() {
    _n += 1;
    if (_n % 3 == 0) {
      loggerService.log(_n.toString());
    }
    nSink.add(_n);
  }

  dispose() {
    _nSubject.close();
  }
}

class LoggerService {
  log(String info) {
    print(info);
  }
}

簡單實現

class GetIt {
  // service 儲存器
  final _factories = Map<Type, dynamic>();

  // 確保不會被constructor
  GetIt._();

  static GetIt _instance;

  static GetIt get instance {
    _instance ??= GetIt._();
    return _instance;
  }

  static GetIt get I => instance;

  T get<T>() {
    return _factories[T];
  }

  void registerSingleton<T>(T instance) {
    _factories[T] = instance;
  }
}

class ServiceA {
  show() {
    print('ServiceA');
  }
}

class ServiceB {
  show() {
    print('ServiceB');
  }
}

main(List<String> args) async {
  GetIt getIt = GetIt.instance;
  getIt.registerSingleton<ServiceA>(ServiceA());
  getIt.registerSingleton<ServiceB>(ServiceB());

  var serviceA = getIt.get<ServiceA>();
  var serviceB = getIt.get<ServiceB>();
  serviceA.show(); // ServiceA
  serviceB.show(); // ServiceB
}