What are the main elements and principles of Dagger in the context of dependency injection?

Dagger is a dependency injection library for Android that helps manage the creation and provision of objects.

Main elements of Dagger:

• @Component — an interface that connects dependency providers (modules) with consumers.
• @Module — a class containing methods annotated with @Provides that create and supply dependencies.
• @Inject — an annotation used to indicate points of dependency injection (e.g., constructors, fields).

Working principle:

1. Modules describe how to create objects.
2. The component assembles these modules and provides dependencies.
3. In usage points (e.g., in Activity or ViewModel), Dagger automatically injects the required objects using @Inject.

Example:

@Module
class NetworkModule {
    @Provides
    fun provideApiService(): ApiService {
        return Retrofit.Builder()...build().create(ApiService::class.java)
    }
}

@Component(modules = [NetworkModule::class])
interface AppComponent {
    fun inject(activity: MainActivity)
}

class MainActivity : AppCompatActivity() {
    @Inject lateinit var apiService: ApiService

    override fun onCreate(savedInstanceState: Bundle?) {
        DaggerAppComponent.create().inject(this)
        super.onCreate(savedInstanceState)
        // apiService is ready to use
    }
}