How to inject an Activity into an Adapter using dagger2

Question

Android Studio 3.0 Canary 8

I am trying to inject my MainActivity into my Adapter. However, my solution works ok, but I think its a code smell and not the right way to do it.

My adapter snippet looks like this the but I don't like about this is that I have to cast the Activity to MainActivity:

public class RecipeAdapter extends RecyclerView.Adapter {
    private List recipeList = Collections.emptyList();
    private Map viewHolderFactories;
    private MainActivity mainActivity;

    public RecipeAdapter(Activity activity, Map viewHolderFactories) {
        this.recipeList = new ArrayList<>();
        this.viewHolderFactories = viewHolderFactories;
        this.mainActivity = (MainActivity)activity;
    }

    @Override
    public RecipeListViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        /* Inject the viewholder */
        final RecipeListViewHolder recipeListViewHolder = viewHolderFactories.get(Constants.RECIPE_LIST).createViewHolder(viewGroup);

        recipeListViewHolder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                /* Using the MainActivity to call a callback listener */
                mainActivity.onRecipeItemClick(getRecipe(recipeListViewHolder.getAdapterPosition()));
            }
        });

        return recipeListViewHolder;
    }
}

In my Module, I pass the Activity in the module's constructor and pass it to the Adapter.

@Module
public class RecipeListModule {
    private Activity activity;

    public RecipeListModule() {}

    public RecipeListModule(Activity activity) {
        this.activity = activity;
    }

    @RecipeListScope
    @Provides
    RecipeAdapter providesRecipeAdapter(Map viewHolderFactories) {
        return new RecipeAdapter(activity, viewHolderFactories);
    }
}

In My Application class I create the components and I am using a SubComponent for the adapter. Here I have to pass the Activity which I am not sure is a good idea.

@Override
public void onCreate() {
    super.onCreate();

    applicationComponent = createApplicationComponent();
    recipeListComponent = createRecipeListComponent();
}

public BusbyBakingComponent createApplicationComponent() {
    return DaggerBusbyBakingComponent.builder()
            .networkModule(new NetworkModule())
            .androidModule(new AndroidModule(BusbyBakingApplication.this))
            .exoPlayerModule(new ExoPlayerModule())
            .build();
}

public RecipeListComponent createRecipeListComponent(Activity activity) {
    return recipeListComponent = applicationComponent.add(new RecipeListModule(activity));
}

My Fragment I inject like this:

@Inject RecipeAdapter recipeAdapter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ((BusbyBakingApplication)getActivity().getApplication())
                .createRecipeListComponent(getActivity())
                .inject(this);
    }

Even though the above design works, I think it's a code smell as I have to cast the Activity to the MainActivity. The reason I use the Activity as I want to make this module more generic.

Just wondering if there is a better way

=============== UPDATE USING INTERFACE

Interface

public interface RecipeItemClickListener {
    void onRecipeItemClick(Recipe recipe);
}

Implementation

public class RecipeItemClickListenerImp implements RecipeItemClickListener {
    @Override
    public void onRecipeItemClick(Recipe recipe, Context context) {
        final Intent intent = Henson.with(context)
                .gotoRecipeDetailActivity()
                .recipe(recipe)
                .build();

        context.startActivity(intent);
    }
}

In my module, I have the following providers

@Module
public class RecipeListModule {
    @RecipeListScope
    @Provides
    RecipeItemClickListener providesRecipeItemClickListenerImp() {
        return new RecipeItemClickListenerImp();
    }

    @RecipeListScope
    @Provides
    RecipeAdapter providesRecipeAdapter(RecipeItemClickListener recipeItemClickListener, Map viewHolderFactories) {
        return new RecipeAdapter(recipeItemClickListener, viewHolderFactories);
    }
}

Then I use it through constructor injection in the RecipeAdapter

public class RecipeAdapter extends RecyclerView.Adapter {
    private List recipeList = Collections.emptyList();
    private Map viewHolderFactories;
    private RecipeItemClickListener recipeItemClickListener;

    @Inject /* IS THIS NESSESSARY - AS IT WORKS WITH AND WITHOUT THE @Inject annotation */
    public RecipeAdapter(RecipeItemClickListener recipeItemClickListener, Map viewHolderFactories) {
        this.recipeList = new ArrayList<>();
        this.viewHolderFactories = viewHolderFactories;
        this.recipeItemClickListener = recipeItemClickListener;
    }

    @Override
    public RecipeListViewHolder onCreateViewHolder(final ViewGroup viewGroup, int i) {
        /* Inject the viewholder */
        final RecipeListViewHolder recipeListViewHolder = viewHolderFactories.get(Constants.RECIPE_LIST).createViewHolder(viewGroup);

        recipeListViewHolder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                recipeItemClickListener.onRecipeItemClick(getRecipe(recipeListViewHolder.getAdapterPosition()), viewGroup.getContext());
            }
        });

        return recipeListViewHolder;
    }
}

Just one question, is the @Inject annotation need for the constructor in the RecipeAdapter. As it works with or without the @Inject.

How to inject an Activity into an Adapter using dagger2

3 Answers