How to @Inject an abstract BaseActivity and its subclasses using dagger.android?

Question

I'm using the new dagger.android package from Dagger 2 to inject Android dependencies in my project.

• I need all my Activities to be a subclass of an abstract BaseActivity

• In my BaseActivity I have member variables to be injected. This way:

  abstract class BaseActivity : AppCompatActivity() {
      @Inject
      lateinit var prefs: MyPreferenceDataStore
      ...// more @Injected members
  }
  

• I do it because I want subclasses of BaseActiviy can have access to injected members of BaseActivity:

  class SubClassActivity : BaseActivity() {
      override fun onCreate(savedInstanceState: Bundle) {                
          val x = prefs.getXXX //use prefs variable from parent class
      }
  }
  

• This is my ApplicationComponent:

  @Singleton @Component(modules = arrayOf(
                  ApplicationModule::class,
                  ActivityBindingModule::class,
                  AndroidSupportInjectionModule::class
              ))
  interface ApplicationComponent {
      @Component.Builder interface Builder {
          @BindsInstance
          fun application(application: Application): Builder
          fun build(): ApplicationComponent
      }
      fun inject(app: AndroidApplication)
  }
  

• The ApplicationModule class has simple @Provides annotated methods:

  @Module
  class ApplicationModule {
      @Singleton @Provides
      fun providesMyPreferenceDataStore(context: Context): MyPreferenceDataStore {
          return MyPreferenceDataStoreImpl(context)
      }
      // more @Provides annotated methods
  }
  

  I think the problem is in my ActivityBindingModule

  @Module
  abstract class ActivityBindingModule {
  
      @PerActivity
      @ContributesAndroidInjector(
          modules = arrayOf(BaseActivityModule::class
      ))
      abstract fun bindBaseActivity(): BaseActivity
  
      @PerActivity
      @ContributesAndroidInjector(
          modules = arrayOf(
              BaseActivityModule::class
      ))
      abstract fun bindSubClassActivity(): SubClassActivity
  }
  

This is what I have tried so far:

• Make the bindSubClassActivity() method not to depend of BaseActivityModule::class, didn't work.

• Move the providesMyPreferenceDataStore from ApplicationModule to the BaseActivityModule, so that the class is:

  @Module
  class BaseActivityModule {
      @PerActivity @Provides
      fun providesMyPreferenceDataStore(context: Context): MyPreferenceDataStore {
          return MyPreferenceDataStoreImpl(context)
      }
  }
  

And this is the error I'm getting:

Error: [dagger.android.AndroidInjector.inject(T)] com.example.BaseActivity cannot
be provided without an @Provides-annotated method.
This type supports members injection but cannot
be implicitly provided.

Answer 1

I didn't understand exactly what you try to do but this solutions based in what i understand

AppComponent should look like this

@Singleton
@Component(modules = [
    AndroidSupportInjectionModule::class,
    AppModule::class,
    ActivityModule::class])
interface AppComponent : AndroidInjector<DaggerApplication> {

    @Component.Builder
    interface Builder {
        @BindsInstance
        fun application(application: Application): Builder

        fun build(): AppComponent
    }
}

your base activity which will inject all the objects

abstract class BaseActivity : DaggerAppCompatActivity() {

    @Inject
    lateinit var prefs: SharedPreferences

    //other objects to inject

}

The activity that will inherit from it eg:MainActivity

class MainActivity : BaseActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        prefs.getBoolean("s", true)
    }

}

And Activity module

@Module
abstract class ActivityModule {

    @ContributesAndroidInjector
    abstract fun bindMainActivity(): MainActivity

    @ContributesAndroidInjector
    abstract fun bindBaseActivity():BaseActivity

}

AppModule

@Module
class AppModule {

    @Singleton
    @Provides
    fun providesMyPreferenceDataStore(application: Application): SharedPreferences {
        return application.getSharedPreferences("test", Context.MODE_PRIVATE)
    }

}