Android Activity Inheritance with Dagger 2

Setting up Dagger 2 injection for inheritance situations with Android activities or fragments can be a pain. This article explains it simply with an example.

Suppose you have a BaseActivity that you need to extend. Let’s call the extending class SubClassedActivity.

Steps

First, contribute the android injector for the subclassed activity.

@Module
abstract class UiModule {
    
    @[ActivityScope ContributesAndroidInjector(modules = [SubClassedActivityModule::class])]
    abstract fun contributeSubClassedActivityInjector(): SubClassedActivity
}

Define the baseActivityModule.

@Module
abstract class BaseActivityModule {
    @Binds
    abstract fun bindBaseActivity(instance: BaseActivity): FragmentActivity
}

Install the BaseActivityModulein the SubClassedActivityModule.

@Module(includes = [BaseActivityModule::class])
abstract class SubClassedActivityModule {

    @Binds
    abstract fun bindSubClassedActivity(instance: SubClassedActivity): BaseActivity

Now, let’s define the BaseActivity.

abstract class BaseActivity : Activity(), HasAndroidInjector {
    @Inject
    lateinit var fragmentInjector: DispatchingAndroidInjector<Any>

    override fun androidInjector(): AndroidInjector<Any> = fragmentInjector

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

Finally, define the SubClassedActivity.

class SubClassedActivity : BaseActivity() {
    // no need to call AndroidInjector.inject(this)
}

Please consider supporting me so I can bring you more content: