Dependency injection using hilt on singleton private constructor class

Question

I'm new to hilt. So i want to try dependency injection with hilt on my project which use MVVM architecture. The structure look like this: JsonHelper -> RemoteDataSource -> Repository -> ViewModel.

The problems occur when i try to inject my DI on RemoteDataSource and Repository since these classes are singleton class and have a private constructor. The error codes look like this

..location\RemoteDataSource.java:40: error: Dagger does not support injection into Kotlin objects
public static final class Companion {

..location\Repository.java:30: error: Dagger does not support injection into Kotlin objects
public static final class Companion {

And these are my RemoteDataSource and Repository codes, i have tried injecting it on the constructor but it says Dagger can't inject on private constructors so then i tried to inject it on the function but still didn't work

RemoteDataSource.kt

@Singleton
class RemoteDataSource private constructor(private val jsonHelper: JsonHelper) {

companion object {

    @Volatile
    private var instance: RemoteDataSource? = null

    @Inject
    fun getInstance(jsonHelper: JsonHelper): RemoteDataSource =
        instance ?: synchronized(this) {
            instance ?: RemoteDataSource(jsonHelper).apply { instance = this }
        }

}

fun getAllRemoteMovies(moviesCallback: LoadMoviesCallback) {
    moviesCallback.onAllMoviesReceived(jsonHelper.loadRemoteMovies())
}

fun getAllRemoteTVShows(tvshowCallback: LoadTVShowCallback) {
    tvshowCallback.onAllTVShowsReceived(jsonHelper.loadRemoteTVShows())
}

interface LoadMoviesCallback {
    fun onAllMoviesReceived(moviesResponses: ArrayList<MovieItem>)
}

interface LoadTVShowCallback {
    fun onAllTVShowsReceived(tvshowResponses: ArrayList<TVShowItem>)
}

}

Repository.kt

@Singleton
class Repository private constructor(private val remoteDataSource: RemoteDataSource) : DataSource {

companion object {

    @Volatile
    private var instance: Repository? = null

    @Inject
    fun getInstance(remoteDataSource: RemoteDataSource): Repository =
        instance ?: synchronized(this) {
            instance ?: Repository(remoteDataSource).apply { instance = this }
        }

}

override fun getAllRemoteMovies(): LiveData<ArrayList<MovieItem>> {
    val remoteMoviesResult = MutableLiveData<ArrayList<MovieItem>>()
    remoteDataSource.getAllRemoteMovies(object : RemoteDataSource.LoadMoviesCallback {
        override fun onAllMoviesReceived(moviesResponses: ArrayList<MovieItem>) {
            remoteMoviesResult.value = moviesResponses
        }
    })
    return remoteMoviesResult
}

override fun getAllRemoteTVShows(): LiveData<ArrayList<TVShowItem>> {
    val remoteTVShowsResult = MutableLiveData<ArrayList<TVShowItem>>()
    remoteDataSource.getAllRemoteTVShows(object : RemoteDataSource.LoadTVShowCallback {
        override fun onAllTVShowsReceived(tvshowResponses: ArrayList<TVShowItem>) {
            remoteTVShowsResult.value = tvshowResponses
        }
    })
    return remoteTVShowsResult
}

}

And this is my injection module RemoteDataSourceModule.kt

@Module
@InstallIn(ActivityComponent::class)
object RemoteDataSourceModule {

@Singleton
@Provides
fun provideJsonHelper(context: Context): JsonHelper {
    return JsonHelper(context)
}

@Singleton
@Provides
fun provideRemoteDataSource(jsonHelper: JsonHelper): RemoteDataSource {
    return RemoteDataSource.getInstance(jsonHelper)
}

@Singleton
@Provides
fun provideRepository(remoteDataSource: RemoteDataSource): Repository {
    return Repository.getInstance(remoteDataSource)
}

}

So how can i solve this problem without changing the class constructor to public?

Like the error says, you can't inject into Kotlin objects. There is also no need, you can specify singletons with Hilt anyway. — Henry Twist, May 09 '21 at 02:47

score 17 · Accepted Answer · answered May 09 '21 at 23:48

@Singleton annotation is enough to notify that the class is a singleton class, so i just remove the companion object and changes private constructor with a public constructor so the code will look like this:

@Singleton
class RemoteDataSource @Inject constructor(private val jsonHelper: JsonHelper) {
    // Your codes
}

Dependency injection using hilt on singleton private constructor class

1 Answers1