无法在RecyclerView中填充任何卡片，可能的原因是什么？

Question

我正在尝试在CardView内填充RecyclerView。虽然我能够记录所有适配器值（以确保它们非空），但我无法在UI中填充任何值。这是活动代码：

FoodActivity.class

public class FoodActivity extends AppCompatActivity
{
    private RecyclerView foodView;
    private List<Result> adapter_data;
    private CustomPlacesAdapter adapter;
    private LinearLayoutManager llm;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_food);
        foodView = (RecyclerView)findViewById(R.id.foodRView);
        adapter = new CustomPlacesAdapter(adapter_data);
        adapter_data = new ArrayList<>();
        llm = new LinearLayoutManager(this);
        foodView.setLayoutManager(llm);
        foodView.setAdapter(adapter);
        doGetRequest("restaurants in los angeles airport");
    }

    private  void doGetRequest(final String message)
    {
        ApiInterfacePlaces apiService =
                ApiClientPlaces.getClient().create(ApiInterfacePlaces.class);

        Call<PlacesPojo> call = apiService.getValues(message, Util.getKeyForPlaces());
        call.enqueue(new Callback<PlacesPojo>()
        {
            @Override
            public void onResponse(Call<PlacesPojo>call, Response<PlacesPojo> response)
            {
                try
                {
                    Log.e("TAG",""+response.body().toString());

                    List<Result> response_res = response.body().getResults();

                    adapter_data = response_res;
                    adapter.notifyDataSetChanged();
                }
                catch (Exception e)
                {
                    Toast.makeText(FoodActivity.this, "Check data connection", Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onFailure(Call<PlacesPojo> call, Throwable t) {
                // Log error here since request failed
                Log.e("FAILURE", t.toString());
            }
        });
    }
}

以下是RecyclerView适配器的代码：

CustomPlacesAdapter.class

public class CustomPlacesAdapter extends RecyclerView.Adapter<CustomPlacesAdapter.HotelsViewHolder>
{   

    private DataHolder d2 = new DataHolder();

    public class HotelsViewHolder extends RecyclerView.ViewHolder
    {
        private TextView hotelName;
        private Typeface face;
        private ImageView hotel_logo;
        private Context mcontext;

        HotelsViewHolder(View itemView)
        {
            super(itemView);
            mcontext = itemView.getContext();
            hotelName = (TextView)itemView.findViewById(R.id.hotelName);
            face = Typeface.createFromAsset(itemView.getContext().getAssets(), "Fonts/Roboto-Regular.ttf");
            hotelName.setTypeface(face);
            hotel_logo = (ImageView)itemView.findViewById(R.id.logoOfHotel);
        }           
    }

    private static class DataHolder
    {
        List<Result> feeds;    
    }   


    public CustomPlacesAdapter(List<Result> feeds)
    {
        this.d2.feeds = feeds;
    }   

    @Override
    public void onAttachedToRecyclerView(RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);
    }    

    @Override
    public HotelsViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.food_item, viewGroup, false);
        HotelsViewHolder pvh = new HotelsViewHolder(v);
        return pvh;
    }

    @Override
    public void onBindViewHolder(HotelsViewHolder feedViewHolder, int i)
    {
        feedViewHolder.hotelName.setText(d2.feeds.get(i).getName());
        Picasso.with(feedViewHolder.mcontext).load(d2.feeds.get(i).getIcon()).into(feedViewHolder.hotel_logo);

    }

    @Override
    public int getItemCount()
    {    
        if(d2.feeds!=null)
        {
            return d2.feeds.size();
        }
        else
        {
            return 0;
        }
    }

}

这是我使用的CardView：

food_item.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_centerHorizontal="true"
    app:cardCornerRadius="5dp"
    android:layout_height="100dp"
    card_view:cardUseCompatPadding="false"
    android:id="@+id/cv">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <ImageView
            android:id="@+id/logoOfHotel"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <TextView
            android:id="@+id/hotelName"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    </RelativeLayout>

</android.support.v7.widget.CardView>

交叉检查了很多东西，仍然无法解决问题，可能是什么导致了这个问题？任何帮助将不胜感激。