Question

我试图学习如何在flutter项目中设置依赖项注入，但是我遇到了一个问题：

I/flutter (14507): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (14507): The following assertion was thrown building _InheritedProviderScope<NumberTriviaBloc>(value: null):
I/flutter (14507): No type GetConcreteNumberTrivia is registered inside GetIt.
I/flutter (14507):  Did you forget to pass an instance name?
I/flutter (14507): (Did you accidentally do  GetIt sl=GetIt.instance(); instead of GetIt sl=GetIt.instance;did you
I/flutter (14507): forget to register it?)
I/flutter (14507): 'package:get_it/get_it_impl.dart':
I/flutter (14507): Failed assertion: line 251 pos 14: 'instanceFactory != null'
I/flutter (14507): 
I/flutter (14507): The relevant error-causing widget was:
I/flutter (14507):   _InheritedProviderScope<NumberTriviaBloc>

依赖初始化：

final sl = GetIt.instance;

void init() {
  //! Features - Number Trivia
  //* Bloc
  sl.registerFactory<NumberTriviaBloc>(() => NumberTriviaBloc(concrete: sl(), inputConverter: sl(), random: sl()));

  //* Use cases
  sl.registerLazySingleton<UseCase<NumberTrivia, Params>>(() => GetConcreteNumberTrivia(sl()));
  sl.registerLazySingleton<UseCase<NumberTrivia, NoParams>>(() => GetRandomNumberTrivia(sl()));

  //* Repository
  sl.registerLazySingleton<NumberTriviaRepository>(() => NumberTriviaRepositoryImplementation(
      localDataSource: sl(), networkInfo: sl(), remoteDataSource: sl()));

  //* Data sources
  sl.registerLazySingleton<NumberTriviaRemoteDataSource>(
      () => NumberTriviaRemoteDataSourceImpl(client: sl()));

  sl.registerLazySingleton<NumberTriviaLocalDataSource>(
      () => NumberTriviaLocalDataSourceImpl(sharedPreferences: sl()));

  //! Core
  sl.registerLazySingleton<InputConverter>(() => InputConverter());
  sl.registerLazySingleton<NetworkInfo>(() => NetworkInfoImpl(sl()));

  //! External
  sl.registerLazySingletonAsync<SharedPreferences>(() => SharedPreferences.getInstance());
  sl.registerLazySingleton<http.Client>(() => http.Client());
  sl.registerLazySingleton<DataConnectionChecker>(() => DataConnectionChecker());
}

我不明白是什么问题，这是其他内容初始化的代码：

class NumberTriviaBloc extends Bloc<NumberTriviaEvent, NumberTriviaState> {
  final GetConcreteNumberTrivia getConcreteNumberTrivia;
  final GetRandomNumberTrivia getRandomNumberTrivia;
  final InputConverter inputConverter;

  NumberTriviaBloc(
      {@required GetConcreteNumberTrivia concrete,
      @required GetRandomNumberTrivia random,
      @required this.inputConverter})
      : assert(concrete != null),
        assert(random != null),
        assert(inputConverter != null),
        getConcreteNumberTrivia = concrete,
        getRandomNumberTrivia = random;
  ...
}

class GetConcreteNumberTrivia implements UseCase<NumberTrivia, Params>{
  final NumberTriviaRepository repository;

  GetConcreteNumberTrivia(this.repository);

  @override
  Future<Either<Failure, NumberTrivia>> call(Params params) async {
    return await repository.getConcreteNumberTrivia(params.number);
  }
}

class GetRandomNumberTrivia implements UseCase<NumberTrivia, NoParams> {
  final NumberTriviaRepository repository;

  GetRandomNumberTrivia(this.repository);

  @override
  Future<Either<Failure, NumberTrivia>> call(NoParams params) async {
    return await repository.getRandomNumberTrivia();
  }
}

class NumberTriviaRepositoryImplementation implements NumberTriviaRepository {
  final NumberTriviaRemoteDataSource remoteDataSource;
  final NumberTriviaLocalDataSource localDataSource;
  final NetworkInfo networkInfo;

  NumberTriviaRepositoryImplementation(
      {@required this.remoteDataSource,
      @required this.localDataSource,
      @required this.networkInfo});
  ...
}

class NumberTriviaRemoteDataSourceImpl implements NumberTriviaRemoteDataSource {
  final http.Client client;

  NumberTriviaRemoteDataSourceImpl({@required this.client});
  ...
}

class NumberTriviaLocalDataSourceImpl implements NumberTriviaLocalDataSource {
  final SharedPreferences sharedPreferences;

  NumberTriviaLocalDataSourceImpl({@required this.sharedPreferences});
  ...
}

class InputConverter {}

class NetworkInfoImpl extends NetworkInfo {
  final DataConnectionChecker connectionChecker;

  NetworkInfoImpl(this.connectionChecker);
  ...
}

小部件是：

void main() {
  di.init();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primaryColor: Colors.green.shade800,
        accentColor: Colors.green.shade600,
      ),
      home: NumberTriviaPage(),
    );
  }
}

class NumberTriviaPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Number Trivia'),
      ),
      body: SingleChildScrollView(child: buildBody(context)),
    );
  }

  BlocProvider<NumberTriviaBloc> buildBody(BuildContext context) {
    return BlocProvider<NumberTriviaBloc>(
      create: (_) => sl<NumberTriviaBloc>(),
      child: Center(
        child: Padding(
          padding: const EdgeInsets.all(10),
          child: Column(
            children: <Widget>[
              SizedBox(
                height: 10,
              ),
              BlocBuilder<NumberTriviaBloc, NumberTriviaState>(
                // ignore: missing_return
                builder: (context, state) {
                  if (state is Empty) {
                    return MessageDisplay(
                      message: 'Start searching',
                    );
                  } else if (state is Loading) {
                    return LoadingWidget();
                  } else if (state is Loaded) {
                    return TriviaDisplay(
                      numberTrivia: state.trivia,
                    );
                  } else if (state is Error) {
                    return MessageDisplay(
                      message: state.message,
                    );
                  }
                },
              ),
              SizedBox(
                height: 20,
              ),
              TriviaControl()
            ],
          ),
        ),
      ),
    );
  }
}

我不知道为什么这对我不起作用。我遵循了youtube上的教程，并且还在github存储库上检查了该教程中的代码，但这对我没有帮助。那你能告诉我发生了什么吗？

在tnc1997的帮助下，我收到了一个新错误：

lib/injection_container.dart:27:91: Error: The argument type 'NumberTriviaRepository/*1*/' can't be assigned to the parameter type 'NumberTriviaRepository/*2*/'.
 - 'NumberTriviaRepository/*1*/' is from 'package:clean_architecture/features/number_trivia/domain/repositories/number_trivia_repository.dart' ('lib/features/number_trivia/domain/repositories/number_trivia_repository.dart').
 - 'NumberTriviaRepository/*2*/' is from 'lib/features/number_trivia/domain/repositories/number_trivia_repository.dart'.
  sl.registerLazySingleton<UseCase<NumberTrivia, NoParams>>(() => GetRandomNumberTrivia(sl<NumberTriviaRepository>()));

这是同一文件，下面一行使用相似的合同

//* Use cases
  sl.registerLazySingleton<UseCase<NumberTrivia, Params>>(() => GetConcreteNumberTrivia(sl<NumberTriviaRepository>()));
  sl.registerLazySingleton<UseCase<NumberTrivia, NoParams>>(() => GetRandomNumberTrivia(sl<NumberTriviaRepository>()));

  //* Repository
  sl.registerLazySingleton<NumberTriviaRepository>(() => NumberTriviaRepositoryImplementation(
      localDataSource: sl<NumberTriviaLocalDataSource>(), networkInfo: sl<NetworkInfo>(), remoteDataSource: sl<NumberTriviaRemoteDataSource>()));

现在我比以前更加困惑

Answer 1

我非常确定，在使用GetIt包时，您需要依赖于接口，而不是构造函数中的具体类型。毕竟，依赖项注入的原理之一是依赖于接口而不是实现，因此可以轻松切换实现。我在下面添加了一个代码示例，显示了如何完成此操作。如果您尚未查看文档here，请获取更多信息和代码示例。如果您对代码示例有任何疑问，请随时发表评论！

class NumberTriviaBloc extends Bloc<NumberTriviaEvent, NumberTriviaState> {
  final UseCase<NumberTrivia, Params> getConcreteNumberTrivia;
  final UseCase<NumberTrivia, NoParams> getRandomNumberTrivia;
  final InputConverter inputConverter;

  NumberTriviaBloc(
      {@required UseCase<NumberTrivia, Params> concrete,
      @required UseCase<NumberTrivia, NoParams> random,
      @required this.inputConverter})
      : assert(concrete != null),
        assert(random != null),
        assert(inputConverter != null),
        getConcreteNumberTrivia = concrete,
        getRandomNumberTrivia = random;
  ...
}

sl.registerFactory<NumberTriviaBloc>(() => NumberTriviaBloc(concrete: sl<UseCase<NumberTrivia, Params>>(), inputConverter: sl<InputConverter>(), random: sl<UseCase<NumberTrivia, NoParams>>()));

使用get_it进行Flutter依赖项注入设置问题

1 个答案: