Dagger：如果没有 @Inject 构造函数或 @Provides-annotated 方法，则无法提供

Question

我正在尝试将我的 MainActivity 的上下文注入到一个方法中。这是我的 Dagger 设置的简化版本：

AppComponent

@Singleton
@Component(
    modules = [
        AndroidInjectionModule::class,
        AppModule::class,
        MainActivityModule::clas
    ]
)
interface AppComponent : AndroidInjector<MyApp> {
    @Component.Builder
    interface Builder {
        @BindsInstance
        fun application(application: Application): Builder

        fun build(): AppComponent
    }
}

AppModule

class AppModule {
    @Singleton
    @Provides
    fun provideRepository(context: Context) = Repository(context)
}

MainActivityModule

@Suppress("unused")
@Module
abstract class MainActivityModule {
    @ContributesAndroidInjector
    abstract fun contributeMainActivity(): MainActivity


    @Binds
    abstract fun bindsMainActivityContext(mainActivity: MainActivity): @ActivityContext Context
}

如您在 provideRepository() 中所见，应该注入一个参数上下文。每当我构建应用程序时，都会出现以下错误：

error: [Dagger/MissingBinding] app.example.myapp.MainActivity cannot be provided without an @Inject constructor or an @Provides-annotated method. This type supports members injection but cannot be implicitly provided.
public abstract interface AppComponent extends dagger.android.AndroidInjector<app.example.myapp.MyApp> {
                ^
  A binding with matching key exists in component: app.example.myapp.injection.module.MainActivityModule_ContributeMainActivity.MainActivitySubcomponent
      app.example.myapp.MainActivity is injected at
          app.example.myapp.injection.module.MainActivityModule.bindsMainActivityContext(mainActivity)
      @app.example.myapp.injection.module.ActivityContext android.content.Context is injected at
          app.example.myapp.injection.module.AppModule.provideTokenRepository(…, context)
      app.example.myapp.repository.interfaces.ITokenRepository is injected at
          app.example.myapp.ui.signin.SignInViewModel(repository)
      app.example.myapp.ui.signin.SignInViewModel is injected at
          app.example.myapp.injection.module.ViewModelModule.bindSignInViewModel(signInViewModel)
      java.util.Map<java.lang.Class<? extends androidx.lifecycle.ViewModel>,javax.inject.Provider<androidx.lifecycle.ViewModel>> is injected at
          app.example.myapp.injection.ViewModelFactory(creators)
      app.example.myapp.injection.ViewModelFactory is injected at
          app.example.myapp.injection.module.ViewModelModule.bindViewModelFactory(factory)
      androidx.lifecycle.ViewModelProvider.Factory is injected at
          app.example.myapp.MainActivity.viewModelFactory
      app.example.myapp.MainActivity is injected at
          dagger.android.AndroidInjector.inject(T) [app.example.myapp.injection.AppComponent → app.example.myapp.injection.module.MainActivityModule_ContributeMainActivity.MainActivitySubcomponent]
  The following other entry points also depend on it:
      dagger.android.AndroidInjector.inject(T) [app.example.myapp.injection.AppComponent → app.example.myapp.injection.module.FragmentModule_ContributeMainFragment.MainFragmentSubcomponent]
      dagger.android.AndroidInjector.inject(T) [app.example.myapp.injection.AppComponent → app.example.myapp.injection.module.FragmentModule_ContributeSignInFragment.SignInFragmentSubcomponent]

正如您从错误中看到的那样，Dagger 似乎能够从上下文跟踪到应用程序的根目录，但由于某种原因我得到了上述错误。

我做错了什么吗？谢谢

Answer 1

您正在尝试从您添加到 AppComponent 的模块中 @Binds MainActivity。那行不通，因为没有 MainActivity（如错误所述）。

@Module
abstract class MainActivityModule {
    @ContributesAndroidInjector
    abstract fun contributeMainActivity(): MainActivity

    // there is no MainActivity here (in AppComponent)
    @Binds
    abstract fun bindsMainActivityContext(mainActivity: MainActivity): @ActivityContext Context
}

您似乎想要做的是将 MainActivity 绑定为 Context in 您的 MainActivity 的子组件，例如像下面这样。您需要第二个模块，然后将 添加到子组件 :

@Singleton
@Component(
    modules = [
        AndroidInjectionModule::class,
        AppModule::class,
        ActivityModule::clas  // bind module with subcomponents instead, see next
    ]
)
interface AppComponent // ...

// Activity module that you can add to AppComponent with subcomponents
@Module
abstract class ActivityModule {

    // bind the module with the bindings here
    @ContributesAndroidInjector(modules = [MainActivityModule::class])
    abstract fun contributeMainActivity(): MainActivity

}

// now we bind it to the MainActivity Subcomponent _only_ and it will work
@Module
abstract class MainActivityModule {

    @Binds
    abstract fun bindsMainActivityContext(mainActivity: MainActivity): @ActivityContext Context
}

Answer 2

根据报错，dagger 不知道如何提供这个依赖，要么你错过了依赖中的@Inject 注解，要么你可能忘记了用@Provides 注解提供依赖

Dagger：如果没有 @Inject 构造函数或 @Provides-annotated 方法，则无法提供

Dagger: cannot be provided without an @Inject constructor or an @Provides-annotated method

android

dependency-injection

kotlin

dagger

dagger-2