Kotlin DI Skill

Dependency Injection with Hilt and Koin.

Topics Covered

Hilt for Android

@HiltAndroidApp
class App : Application()

@Module
@InstallIn(SingletonComponent::class)
object AppModule {
    @Provides @Singleton
    fun provideDatabase(@ApplicationContext context: Context) =
        Room.databaseBuilder(context, AppDatabase::class.java, "app.db").build()

    @Provides
    fun provideUserDao(db: AppDatabase) = db.userDao()
}

@HiltViewModel
class UserViewModel @Inject constructor(
    private val repository: UserRepository
) : ViewModel()

Koin for Multiplatform

val appModule = module {
    single { HttpClient(getEngine()) }
    single { UserRepository(get()) }
    viewModel { UserViewModel(get()) }
}

// Start Koin
startKoin {
    modules(appModule)
}

// Inject
val repository: UserRepository by inject()

Testing with DI

@HiltAndroidTest
class UserViewModelTest {
    @get:Rule val hiltRule = HiltAndroidRule(this)

    @BindValue @JvmField
    val repository: UserRepository = mockk()

    @Inject lateinit var viewModel: UserViewModel

    @Before fun setup() { hiltRule.inject() }
}

Troubleshooting

Issue	Resolution
"No binding for..."	Add @Provides or @Binds
ViewModel not injected	Use hiltViewModel() in Compose

Usage

Skill("kotlin-di")