Dagger：组件中存在具有匹配键的绑定

Question

I am using Dagger 2.16 and was following this article for my dagger implementation. Everything was working fine with this implementation until I had only one Activity(HomeActivity). As soon as I started implementing Dagger in SplashScreenActivity. I started getting this error. Here is some code from my project

AppComponent.kt

@Singleton
@Component(modules = [
    AndroidInjectionModule::class,
    AppModule::class,
    ActivityBuilder::class,
    ServiceBuilder::class,
    BroadcastRecieverBuilder::class])
interface AppComponent : AndroidInjector<MyApp> {
    @Component.Builder
    abstract class Builder : AndroidInjector.Builder<MyApp>()
}

AppModule.kt

@Module()
class AppModule {

    @Provides
    @Singleton
    fun provideContext(application: MyApp): Context {
        return application
    }

    @Provides
    @Singleton
    fun provideRestService(retrofit: Retrofit): RestService {
        return retrofit.create(RestService::class.java)
    }
    ...
}

ActivityBuilder.kt

@Module
abstract class ActivityBuilder {

    @ContributesAndroidInjector(modules = [HomeActivityModule::class])
    @PerActivity
    abstract fun bindHomeActivity(): HomeActivity

    @ContributesAndroidInjector(modules = [SplashScreenModule::class])
    @PerActivity
    abstract fun bindSplashActivity(): SplashScreenActivity
}

BaseActivity.kt

abstract class BaseActivity<V : BaseView, P : MvpBasePresenter<V>> :
        MvpActivity<V, P>(), BaseView, HasSupportFragmentInjector {
    @Inject
    lateinit var fragmentInjector: DispatchingAndroidInjector<Fragment>

    @Inject
    lateinit var mPresenter: P

    override fun onCreate(savedInstanceState: Bundle?) {
        AndroidInjection.inject(this)
        super.onCreate(savedInstanceState)
    }

    override fun createPresenter(): P = mPresenter

    override fun supportFragmentInjector(): AndroidInjector<Fragment> {
        return fragmentInjector
    }
}

I have my own BaseActivity instead of DaggerActivity because I what to inherit from mosby's MvpActivity.

SplashScreenModule.kt

@Module
abstract class SplashScreenModule {

    @Binds
    @PerActivity
    internal abstract fun splashPresenter(splashPresenter: SplashScreenPresenter): BasePresenter<*>
}

HomeActivityModule.kt

@Module
abstract class HomeActivityModule {

    @Binds
    @PerActivity
    internal abstract fun homePresenter(homePresenter: HomeActivityPresenter): BasePresenter<*>

    @ContributesAndroidInjector(modules = [DownloadFragmentModule::class])
    @PerFragment
    internal abstract fun downloadsFragment(): DownloadsFragment
}

Now when I build this, I get an error as follows

error: [Dagger/MissingBinding] [dagger.android.AndroidInjector.inject(T)] java.util.Map<java.lang.Class<? extends android.support.v4.app.Fragment>,javax.inject.Provider<dagger.android.AndroidInjector.Factory<? extends android.support.v4.app.Fragment>>> cannot be provided without an @Provides-annotated method.
public abstract interface AppComponent extends dagger.android.AndroidInjector<com.realtime.app.MyApp> {
                ^
  A binding with matching key exists in component: com.realtime.dagger.ActivityBuilder_BindHomeActivity.HomeActivitySubcomponent
      java.util.Map<java.lang.Class<? extends android.support.v4.app.Fragment>,javax.inject.Provider<dagger.android.AndroidInjector.Factory<? extends android.support.v4.app.Fragment>>> is injected at
          dagger.android.DispatchingAndroidInjector.<init>(injectorFactories)
      dagger.android.DispatchingAndroidInjector<android.support.v4.app.Fragment> is injected at
          com.realtime.core.BaseActivity.fragmentInjector
      com.realtime.splashScreen.SplashScreenActivity is injected at
          dagger.android.AndroidInjector.inject(T)
  component path: com.realtime.dagger.AppComponent → com.realtime.dagger.ActivityBuilder_BindSplashActivity.SplashScreenActivitySubcomponent

I have gone through other similar que like this but couldn't relate it to what I am facing. What am I missing?

Update: For now I am not inheriting BaseActivity in SplashScreenActivity so that I can avoid injecting fragmentInjector: DispatchingAndroidInjector<Fragment> . It is working for now as I don't have any fragment in SplashScreenActivity.

Answer 1

It works for HomeActivity because it binds a fragment:

@ContributesAndroidInjector
fun downloadsFragment(): DownloadsFragment

SplashScreenActivity does not.

---

AndroidInjection uses DispatchingAndroidInjector to handle runtime injections, which basically contains a Map of classes to their component builders. This map needs to be injected like everything else. In the case of HomeActivity the fragment declaration in the module generates a binding for the map, which can then be injected.

Since there is no Fragment on the splash activity Dagger does not know about any bindings, let alone any map. Which is why it complains that it cannot be provided .

You can read more here about multibindings .

To prevent this from happening, you should register AndroidInjectionModule on your AppComponent, which just contains the declarations for the empty maps.

While it contains the declaration for android.app.Fragment it does not for android.support.v4.app.Fragment , which is where the error comes from.

---

So to fix this specific error you should add AndroidSupportInjectionModule to your component, which also includes the support bindings, providing an empty map when there are no fragments in an activity.

@Component(modules = [AndroidSupportInjectionModule::class, /* ... */])
interface AppComponent { /* ... */ }