Android Dagger2依赖成分

在我的应用程序中，我有一个具有应用范围的组件（与Singleton相同），它提供了一个ViewModel工厂，还有一个具有活动范围的依赖组件，它将工厂注入到片段中

应用程序组件的定义如下：

@Component(modules = [AppModule::class, /* other stuff */, ViewModelModule::class])

@ApplicationScope
interface AppComponent {
    fun inject(app: Application)

    /* other stuff */

    val viewModelFactory: ViewModelFactory
}

@ApplicationScope
@Module
abstract class ViewModelModule {
    @Binds
    abstract fun bindViewModelFactory(viewModelFactory: ViewModelFactory): ViewModelProvider.Factory

    @Binds
    @IntoMap
    @ViewModelKey(DisplayEntryViewModelImpl::class)
    abstract fun bindDisplayEntryViewModel(displayEntryViewModelImpl: DisplayEntryViewModelImpl): ViewModel
}

@Component(dependencies = [AppComponent::class], modules = [DisplayEntryActivityModule::class])

@ActivityScope
interface DisplayEntryActivityComponent {
    fun inject(displayEntryActivity: DisplayEntryActivity)
    fun inject(displayEntryFragment: DisplayEntryFragment)
}

视图模型模块定义如下：

@Component(modules = [AppModule::class, /* other stuff */, ViewModelModule::class])

@ApplicationScope
interface AppComponent {
    fun inject(app: Application)

    /* other stuff */

    val viewModelFactory: ViewModelFactory
}

@ApplicationScope
@Module
abstract class ViewModelModule {
    @Binds
    abstract fun bindViewModelFactory(viewModelFactory: ViewModelFactory): ViewModelProvider.Factory

    @Binds
    @IntoMap
    @ViewModelKey(DisplayEntryViewModelImpl::class)
    abstract fun bindDisplayEntryViewModel(displayEntryViewModelImpl: DisplayEntryViewModelImpl): ViewModel
}

@Component(dependencies = [AppComponent::class], modules = [DisplayEntryActivityModule::class])

@ActivityScope
interface DisplayEntryActivityComponent {
    fun inject(displayEntryActivity: DisplayEntryActivity)
    fun inject(displayEntryFragment: DisplayEntryFragment)
}

活动范围组件的定义如下：

@Component(modules = [AppModule::class, /* other stuff */, ViewModelModule::class])

@ApplicationScope
interface AppComponent {
    fun inject(app: Application)

    /* other stuff */

    val viewModelFactory: ViewModelFactory
}

@ApplicationScope
@Module
abstract class ViewModelModule {
    @Binds
    abstract fun bindViewModelFactory(viewModelFactory: ViewModelFactory): ViewModelProvider.Factory

    @Binds
    @IntoMap
    @ViewModelKey(DisplayEntryViewModelImpl::class)
    abstract fun bindDisplayEntryViewModel(displayEntryViewModelImpl: DisplayEntryViewModelImpl): ViewModel
}

@Component(dependencies = [AppComponent::class], modules = [DisplayEntryActivityModule::class])

@ActivityScope
interface DisplayEntryActivityComponent {
    fun inject(displayEntryActivity: DisplayEntryActivity)
    fun inject(displayEntryFragment: DisplayEntryFragment)
}

当我尝试在片段中注入viewmodel工厂时，出现以下错误：

error: android.arch.lifecycle.ViewModelProvider.Factory cannot be provided without an @Provides- or @Produces-annotated method.

如果我更新活动组件以包含视图模型模块，如下所示

@Component(dependencies = [AppComponent::class], modules = [DisplayEntryActivityModule::class, ViewModelModule::class])

@ActivityScope
interface DisplayEntryActivityComponent {
    fun inject(displayEntryActivity: DisplayEntryActivity)
    fun inject(displayEntryFragment: DisplayEntryFragment)
}

然后进行编译。我的理解是，如果父组件显式地提供这些成员，则依赖组件可以从父组件访问注入的成员，就像我在这里使用

 val viewModelFactory: ViewModelFactory

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那么为什么我仍然需要在活动范围组件中提供viewmodel模块呢？

当使用依赖项时，dagger将使用该组件注入成员。
父组件必须显式声明可在子组件中使用的对象

@Component(modules = [AppModule::class, /* other stuff */, ViewModelModule::class])
@ApplicationScope  
interface AppComponent {
   fun inject(app: Application)

   fun viewModelFactory(): ViewModelProvider.Factory

   fun viewModel(): ViewModel
}

您可以看看这篇文章：

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这没什么区别。很抱歉，我返回了错误类型的注入成员。试试这个怎么样？谢谢，这个管用。您是否介意更新您的答案，并简要解释为什么需要这样声明此特定依赖项，或者提供相关信息的链接？