Hilt: Question, How to reuse a module and provide its bindings

We are trying out Hilt for our production project, we have a use case that I’m not sure how Hilt would handle it This is our approach towards providing different bindidngs when resuing a module:

Note I simplified the code below our actual use case has lots of modules and using Qulifiers is not convenient

@Module
class WidgetListModule {

    @Provides
    @FragmentScope
    fun provideCategoryViewModelFactory(
        widgetListDataSource: WidgetListDataSource<*>, // Not provided anywhere, user should provide it
        compositeDisposable: CompositeDisposable,
        threads: Threads,
        alak: Alak,
    ): ViewModelProvider.Factory {
        return viewModelFactory {
            WidgetListViewModel(
                compositeDisposable = compositeDisposable,
                dataSource = widgetListDataSource,
                threads = threads,
                alak = alak,
            )
        }
    }
}

The module that includes this module

@Module(includes = [WidgetListModule::class])
class ManageModule {

    @Provides
    @FragmentScope
    fun provideWidgetListDataSource(
        api: ManagePostAPI
    ): WidgetListDataSource<*> {
        return WidgetListGetDataSource(api::getPage)
    }
}

@FragmentScope
@Subcomponent(modules = [ManageModule::class])
interface ManageFragmentInjector {
    fun inject(manageFragment: ManageFragment)
}

And we have cases that the injector being used to inject a field is determined at run time like this:

override fun inject() {
        if (args.source == "foo") {
            mainActivityComponent.fooFragmentInjector()
                .inject(this)
        } else {
            mainActivityComponent.barFragmentInjector()
                .inject(this)
        }
    }

So my question is how can I resuse a module and provide its dependencies with hilt?

[MRezaNasirloo]

For anyone coming to this issue, the solution provided by @bcorso works with a bit of adjustment, since the injection has not happened yet, you will get an NPE exception if you access the fooWidgetListdataSource so you can’t have @Inject annotation on it like @Inject FooWidgetListdataSource fooWidgetListdataSource; instead, you can access your dependence with an entry point interface

override val widgetListRepository: WidgetListRepository by lazy {
        EntryPoints.get(this, ManageEntryPoint::class.java).manageRepository()
    }

    @EntryPoint
    @InstallIn(FragmentComponent::class)
    interface ManageEntryPoint {

        @Named(MANAGE)
        fun manageRepository(): WidgetListRepository
    }

[bcorso]

Yeah, this is a case where it’s possible to do with Hilt but you will loose a bit of the compile-time guarantees for that binding.

One solution is to provide the implementation from each fragment via an interface and have the @Provides method delegate to the fragment (there’s a similar use case in the migration guide, here). For example:

// Implemented by Fragments that provide a custom WidgetListdataSource.
interface HasWidgetListdataSource {
  WidgetListDataSource getWidgetListDataSource();
}

// Provides the WidgetListDataSource for a specific fragment or null if the fragment doesn't provide it
@Module
@InstallIn(FragmentComponent.class)
interface WidgetListdataSourceModule {
  @Provides
  @Nullable
  WidgetListDataSource provideWidgetListDataSource(Fragment fragment) {
    return (fragment instanceof HasWidgetListdataSource)
        ? ((HasWidgetListdataSource) fragment).getWidgetListDataSource();
        : null; // or DefaultWidgetListDataSource
  }
}

// Provides FooWidgetListdataSource to any dependency requesting WidgetListdataSource
class FooFragment extends HasWidgetListdataSource {
  @Inject FooWidgetListdataSource fooWidgetListdataSource;

  @Override
  WidgetListDataSource getWidgetListDataSource() {
    return fooWidgetListdataSource;
  }
}

// Provides BarWidgetListdataSource to any dependency requesting WidgetListdataSource
class BarFragment extends HasWidgetListdataSource {
  @Inject BarWidgetListdataSource barWidgetListdataSource;

  @Override
  WidgetListDataSource getWidgetListDataSource() {
    return barWidgetListdataSource;
  }
}