IoC

app_context.dart

final getIt = GetIt.instance;
void configure() {
  getIt
    ..registerSingleton(Repository())
    ..registerFactory(
        () => Bloc(getIt<Repository>()));
}

main.dart

import 'app_context.dart';

void main() {
  configure();

  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyPage(),
    );
  }
}

class MyPage extends StatefulWidget {
  @override
  _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> {
  final bloc = getIt<DebtorBloc>();
  
  @override
  void dispose() {
    bloc.close();
    super.dispose();
  }
  
  @override
  Widget build(BuildContext context) {
    // Presentanional Components Composition
  }
}

services.dart

class Repository {}

class Bloc {
  final Repository repository;
  
  ServiceB(this.repository);
}