Dagger2 找不到提供的实例

Question

我在尝试将 Dagger 与多个组件一起使用时遇到了一些问题，我有以下内容（每个 class 在其自己的文件中）：

范围：

@Scope
@Retention(AnnotationRetention.RUNTIME)
annotation class PrototypeScope

模块：

@Module(includes = [RepositoriesModule::class])
class GetRandomBookUseCaseModule {

    @Provides
    @Singleton
    fun provideGetRandomBookUseCase(booksRepository: BooksRepository) =
        GetRandomBookUseCase(booksRepository)
}


@Module
class RepositoriesModule {

    @Provides
    @Singleton
    fun providesBooksRepository(): BooksRepository = BooksRepositoryImpl()

    @Provides
    @Singleton
    fun providesPreferencesRepository(): PreferencesRepository = PreferencesRepositoryImpl()
}


@Module
class BookReaderModule(val ctx: Context) {

    @Provides
    @PrototypeScope
    fun provideBookReader(getRandomBookUseCase: GetRandomBookUseCase) =
        BookReader(ctx, getRandomBookUseCase)
}

组件：

@Component(
    modules = [GetRandomBookUseCaseModule::class]
)
interface UseCasesComponent {

}

@Component(
    dependencies = [UseCasesComponent::class],
    modules = [BookReaderModule::class]
)
@PrototypeScope
interface BookReaderFragmentComponent {

    fun inject(bookReaderFragment: BookReaderFragment)
}

然后，在 BookReaderFragment 中我有以下内容：

class BookReaderFragment : Fragment() {
    @Inject lateinit var bookReader: BookReader
    val component: BookReaderFragmentComponent by lazy {
        DaggerBookReaderFragmentComponent
            .builder()
            .useCasesComponent(DaggerUseCasesComponent.create())
            .bookReaderModule(BookReaderModule(context!!))
            .build()
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        component.inject(this)
        ...
    }

    ...
}

但是，Dagger 应该失败：

error: GetRandomBookUseCase cannot be provided without an @Inject constructor or an @Provides-annotated method.

这是怎么回事？为什么 Dagger 找不到提供的方法？

非常感谢

更新：添加包含在 GetRandomBookUseCaseModule 中的 RepositoriesModule。进行此更改后，我意识到，尽管出现了错误消息，但问题与 BookReader 的注入方式有关。如果我以这种方式从 BookReaderFragment 中删除 @Injected：

class BookReaderFragment : Fragment() {
    lateinit var bookReader: BookReader
    val component: BookReaderFragmentComponent by lazy {
        DaggerBookReaderFragmentComponent
            .builder()
            .useCasesComponent(DaggerUseCasesComponent.create())
            .bookReaderModule(BookReaderModule(context!!))
            .build()
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        component.inject(this)
        ...
    }

    ...
}

然后就没有错误了，但是它不会在运行时运行，但是当设置了@Inject 时，就会抛出错误。

Answer 1

将RepositoriesModule纳入GetRandomBookUseCaseModule

@Module(includes = {RepositoriesModule.class})
class {

    @Provides
    @Singleton
    fun provideGetRandomBookUseCase(booksRepository: BooksRepository) =
        GetRandomBookUseCase(booksRepository)
}

并且组件应该是

@Component(
    modules = [GetRandomBookUseCaseModule::class]
)
interface UseCasesComponent {
    GetRandomBookUseCase getRandomBookUseCase();
}

Answer 2

我终于找到了问题所在：我没有在 UseCasesComponent 中返回 getRandomBookUseCase，最后我将 UseCasesComponent 更改为：

@Component(
    modules = [GetRandomBookUseCaseModule::class]
)
@Singleton
interface UseCasesComponent {

    val getRandomBookUseCase: GetRandomBookUseCase
}

和 BookReaderComponent 到：

@Component(
    dependencies = [UseCasesComponent::class],
    modules = [BookReaderModule::class]
)
@PrototypeScope
interface BookReaderFragmentComponent {

    val bookReader: BookReader
}

然后在片段中我将其用作：

class BookReaderFragment : Fragment() {
    lateinit var bookReader: BookReader
    val component: BookReaderFragmentComponent by lazy {
        DaggerBookReaderFragmentComponent
            .builder()
            .useCasesComponent(DaggerUseCasesComponent.create())
            .bookReaderModule(BookReaderModule(context!!))
            .build()
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        bookReader = component.bookReader
        ...
    }

    ...
}

非常感谢你的帮助，你真的帮了我很多，解决了我的问题。

Dagger2 找不到提供的实例

Dagger2 not finding provided instance

android

dagger

dagger-2