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Multi-Module Android Apps

docs/reference/koin-android/multi-module.md

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This guide covers Android-specific aspects of multi-module architecture with Koin.

:::info For core module concepts (includes(), organization, overrides), see Modules. :::

Android Application Setup

With Annotations

kotlin
@KoinApplication(AppModule::class)
class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()

        startKoin<MyApplication> {
            androidLogger()
            androidContext(this@MyApplication)
        }
    }
}

// Root module includes all features
@Module(includes = [LoginModule::class, HomeModule::class, ProfileModule::class])
class AppModule

With DSL

kotlin
class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()

        startKoin {
            androidLogger()
            androidContext(this@MyApplication)
            modules(appModule)  // Single root module
        }
    }
}

// Root module includes all features
val appModule = module {
    includes(
        loginModule,
        homeModule,
        profileModule
    )
}

Feature Module Example

kotlin
// :feature:login module
@KoinViewModel
class LoginViewModel(
    private val loginUseCase: LoginUseCase,
    private val userRepository: UserRepository
) : ViewModel()

@Factory
class LoginUseCase(private val authService: AuthService)

@Module(includes = [DataModule::class])
@ComponentScan("com.app.feature.login")
class LoginModule
kotlin
// DSL equivalent
val loginModule = module {
    includes(dataModule)
    viewModel<LoginViewModel>()
    factory<LoginUseCase>()
}

Dynamic Feature Loading

Load feature modules on-demand with Activity lifecycle:

kotlin
class FeatureActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        loadKoinModules(featureModule)
        super.onCreate(savedInstanceState)
    }

    override fun onDestroy() {
        super.onDestroy()
        unloadKoinModules(featureModule)
    }
}

Koin vs Hilt Comparison

HiltKoin
@HiltAndroidAppstartKoin { androidContext() }
@InstallIn(SingletonComponent)Module loaded in startKoin {}
@EntryPoint for cross-moduleAutomatic resolution
Component dependenciesincludes()
@ApplicationContextandroidContext() (automatic)

:::info Koin Advantage: No @EntryPoint interfaces needed. Dependencies resolve across modules automatically as long as all modules are loaded. :::

Android Testing

Test Module in Isolation

kotlin
class LoginViewModelTest : KoinTest {

    @get:Rule
    val koinTestRule = KoinTestRule.create {
        modules(
            loginModule,
            module {
                single<UserRepository> { mockk() }
                single<AuthService> { mockk() }
            }
        )
    }

    private val viewModel: LoginViewModel by inject()

    @Test
    fun `test login`() {
        // Test with mocked dependencies
    }
}

Verify All Modules

kotlin
class ModuleCheckTest : KoinTest {

    @Test
    fun `verify all modules`() {
        appModule.verify()  // Verifies included modules too
    }
}

See Also