Dagger - MissingBinding Map,Provider> cannot be provided without an @Provides-annotated method

Question

I'm just starting with Dependency Injection using Dagger Framework, so it might be I'm missing something trivial, but I've spent more than 2 days just going over the code and the tutorial.

So, I am trying to use dagger dependency injection for my ViewModels, I found that I could do that with a feature called multi binding, which I've implemented. I have an AppComponent and an ActivitySubComponent. The AppComponent installs a ViewModelFactoryModule which @Binds a ViewModelProvider.Factory, I want this Module in the Application because I think it should be independent of the Activity life-cycle. And in my ActivitySubComponent I have a ViewModelsModule which @Binds a ViewModel.

Now per my understanding I have included ActivitySubComponent in the ViewModelFactoryModule which will add the subcomponent to the AppComponent.

Edit :

Now when I make/build the project I get the following error. Apologies, the original error was:

error: [Dagger/MissingBinding] java.util.Map<java.lang.Class<? extends androidx.lifecycle.ViewModel>,javax.inject.Provider<androidx.lifecycle.ViewModel>> cannot be provided without an @Provides-annotated method.
java.util.Map<java.lang.Class<? extends androidx.lifecycle.ViewModel>,javax.inject.Provider<androidx.lifecycle.ViewModel>> is injected at
com.mobile.presentation.viewmodels.build.ViewModelFactory(creators)
com.mobile.presentation.viewmodels.build.ViewModelFactory is provided at
com.mobile.app.AppComponent.obtainViewModelsFactory()

The following error was produced after adding following method to AppComponent.java Map<Class<? extends ViewModel>, Provider<ViewModel>> obtainMap();.

error: [Dagger/MissingBinding] java.util.Map<java.lang.Class<? extends androidx.lifecycle.ViewModel>,javax.inject.Provider<androidx.lifecycle.ViewModel>> cannot be provided without an @Provides-annotated method.
java.util.Map<java.lang.Class<? extends androidx.lifecycle.ViewModel>,javax.inject.Provider<androidx.lifecycle.ViewModel>> is provided at
com.mobile.app.AppComponent.obtainMap()
It is also requested at:
com.mobile.presentation.viewmodels.build.ViewModelFactory(creators)
The following other entry points also depend on it:
com.mobile.app.AppComponent.obtainViewModelsFactory()

---

Enough jibber jabber, here is the relevant code:

AppComponent.java

@AppScope
@Component(
        modules = {
                AppModule.class,
                ViewModelFactoryModule.class
        })
public interface AppComponent {
    App obtainApp();

    ViewModelFactory obtainViewModelsFactory();

    // I tried with adding the following line, out of sheer annoyance.
    // Map<Class<? extends ViewModel>, Provider<ViewModel>> obtainMap();
}

ViewModelFactoryModule.java

@Module(subcomponents = ActivitySubComponent.class)
public abstract class ViewModelFactoryModule {
    @AppScope
    @Binds
    public abstract ViewModelProvider.Factory bindViewModelFactory(ViewModelFactory viewModelFactory);
}

ViewModelsFactory.java

@AppScope
public class ViewModelFactory implements ViewModelProvider.Factory {

    private final Map<Class<? extends ViewModel>, Provider<ViewModel>> creators;

    @Inject
    public ViewModelFactory(Map<Class<? extends ViewModel>, Provider<ViewModel>> creators) {
        this.creators = creators;
    }

    @SuppressWarnings("unchecked")
    @NonNull
    @Override
    public <T extends ViewModel> T create(@NonNull Class<T> modelClass)
    {
        Provider<? extends ViewModel> creator = creators.get(modelClass);
        if (creator == null) {
            for (Map.Entry<Class<? extends ViewModel>, Provider<ViewModel>> entry : creators.entrySet()) {
                if (modelClass.isAssignableFrom(entry.getKey())) {
                    creator = entry.getValue();
                    break;
                }
            }
        }

        if (creator == null) {
            throw new IllegalArgumentException("unknown model class " + modelClass);
        }

        try {
            return (T) creator.get();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

ActivitySubComponent.java

// I have a separate module for my `LiveData`.
@ActivityScope
@Subcomponent(
        modules = {
                ActivityModule.class,
                ViewModelsModule.class,
                SplashLiveDataModule.class
        }
)
public interface ActivitySubComponent {

    Activity obtainActivity();

    LiveData<InitialAPIResponse> obtainLiveInitialApiResponse();

    LiveData<InitialSplashApiStatus> obtainLiveInitialSplashApiStatus();

    @Subcomponent.Builder
    interface Builder {
        ActivitySubComponent build();

        Builder setActivityModule(ActivityModule activityModule);
    }
}

ViewModelsModule.java

@Module
public abstract class ViewModelsModule {

    @ActivityScope
    @Binds
    @IntoMap
    @ViewModelKey(SplashViewModel.class)
    public abstract ViewModel provideVideoListViewModel(SplashViewModel viewModel);
}

Now, I understand from this that the AppComponent cannot have direct access to ActivitySubComponent, but it should be able to access the SubComponent since a @Subcomponent is generated as an inner class of the component (perhaps I'm missing something), and I don't think ViewModels should be bound to the application's component (I say this because if I move my ViewModelsModule to the AppComponent too I can run the code and everything works right), am I wrong in my logical approach?

dagger dependencies:

implementation 'com.google.dagger:dagger:2.22'
annotationProcessor 'com.google.dagger:dagger-compiler:2.22'

Answer 1

You are right. Adding ActivitySubComponent in the ViewModelFactoryModule will add the subcomponent to the AppComponent.

When you want to add subcomponent to parent, you have two way of doing. First by adding subcomponent in a module and then adding that module to parent. Second, by declaring an abstract method in parent component that returns subcomponent.

You got first part right but in your AppComponent, you have created a method that returns ViewModelFactory which is already provided by ViewModelFactoryModule. This conflicts with object graph and due to that your build fails. You need to remove both methods that return ViewModelFactory and Map and this will fix the problem.