Dagger2在视图模型中注入导航器

Question

I am using Android's ViewModel lib and I want to inject a Navigator in a ViewModel which is scoped inside App, but my navigator is dependent of activity. I don't know how to inject it. I'll copy and paste some files here but my project can be found here and the files I mention is under 'app/src/main/java/app/vehiclemonitor/' + 'app/' or 'viewmodel' or 'features/home'

VmAppComponent.java

@Singleton
@Component(modules = {VMAppModule.class, VMApiServiceModule.class, SchedulerModule.class, ViewModelModule.class})
public interface VMAppComponent {

    void inject(VMApp app);

    HomeActivityComponent injectHomeActivity(BaseActivityModule module);

    AddEditVehicleActivityComponent injectAddEditVehicleActivity(BaseActivityModule module);
}

ViewModelModule.class

@Module
public abstract class ViewModelModule {

    @Binds
    @IntoMap
    @ViewModelKey(HomeViewModel.class)
    abstract ViewModel bindHomeViewModel(HomeViewModel homeViewModel);

    @Binds
    abstract ViewModelProvider.Factory bindViewModelFactory(ViewModelFactory factory);

}


public class HomeViewModel extends ViewModel {

    @NonNull    
    private HomeNavigator navigationProvider;

    @NonNull
    private BaseSchedulerProvider schedulerProvider;

    @Inject
    public HomeViewModel(@NonNull final BaseSchedulerProvider schedulerProvider) {
        this.schedulerProvider = schedulerProvider;
    }

    // @Inject
    // public HomeViewModel(@NonNull HomeNavigator navigationProvider, @NonNull BaseSchedulerProvider schedulerProvider) {
    //  this.navigationProvider = navigationProvider;
    //  this.schedulerProvider = schedulerProvider;
    // }

    void handleAddButtonClick() {
        navigationProvider.addNewVehicle();
    }

    public void setNavigationProvider(final HomeNavigator navigationProvider) {
        this.navigationProvider = navigationProvider;
    }
}

Answer 1

First of all, this is a good question, a lot of developers had/have the same question and currently there isn't an official solution to this.

The only sure thing is:

A ViewModel should not have references to Activities or Views in general.

What you should do is reading all this thread in GitHub https://github.com/googlesamples/android-architecture-components/issues/63 , a lot of solutions have been posted and probably there is at least one good for you.

About the link you posted on googlesamples and blueprint , their Navigator is not good as you can think. It's still an example app and probably they removed some complexity to make the sample easier to understand for a wider set of developers.

I think a better approach is the one provided in this sample repo which completely remove references to Activities. (It's made in Kotlin, I don't know if you can emulate the same behaviours with Java but you could try at least).