ViewModelProviders with Dagger 2, not able to grasp the concept

Question

I have a Retrofit Service like this

public interface BrandsService {
    @GET(\"listBrand\")
    Call> getBrands();
}

Answer 1

EDIT: An important note. To use Jetpack ViewModel, you don't need map-multibinding. Read on.

---

The answer can be simpler than Mumi's approach, which is that you expose the ViewModel on your component:

@Singleton
@Component(modules={...})
public interface SingletonComponent {
    BrandsViewModel brandsViewModel();
}

And now you can access this method on the component inside the ViewModelFactory:

// @Inject
BrandsViewModel brandsViewModel;

...
brandsViewModel = new ViewModelProvider(this, new ViewModelProvider.Factory() {
    @Override
    public  create(Class modelClazz) {
        if(modelClazz == BrandsViewModel.class) {
            return singletonComponent.brandsViewModel();
        }
        throw new IllegalArgumentException("Unexpected class: [" + modelClazz + "]");
    }).get(BrandsViewModel.class);

---

All this can be simplified and hidden with Kotlin:

inline fun  AppCompatActivity.createViewModel(crossinline factory: () -> T): T = T::class.java.let { clazz ->
    ViewModelProvider(this, object: ViewModelProvider.Factory {
        override fun  create(modelClass: Class): T {
            if(modelClass == clazz) {
                @Suppress("UNCHECKED_CAST")
                return factory() as T
            }
            throw IllegalArgumentException("Unexpected argument: $modelClass")
        }
    }).get(clazz)
}

which now lets you do

brandsViewModel = createViewModel { singletonComponent.brandsViewModel() }

Where now BrandsViewModel can receive its parameters from Dagger:

class BrandsViewModel @Inject constructor(
    private val appContext: Context,
    /* other deps */
): ViewModel() {
    ...
}

Though the intent might be cleaner if a Provider is exposed from Dagger instead

interface SingletonComponent {
    fun brandsViewModel(): Provider
}

brandsViewModel = createViewModel { singletonComponent.brandsViewModel().get() }

---

With some additional trickery coming in from android-ktx, you could even do

@Suppress("UNCHECKED_CAST")
inline fun  Fragment.fragmentViewModels(
    crossinline creator: () -> T
): Lazy {
    return createViewModelLazy(T::class, storeProducer = {
        viewModelStore
    }, factoryProducer = {
        object : ViewModelProvider.Factory {
            override fun  create(
                modelClass: Class
            ): T = creator.invoke() as T
        }
    })
}

And then

class ProfileFragment: Fragment(R.layout.profile_fragment) {
    private val viewModel by fragmentViewModels {
        singletonComponent.brandsViewModelFactory().get()
    }

Where brandsViewModelFactory() is

fun brandsViewModelFactory(): Provider