我是java初学者。
我正在使用firestore recyclerview，我想计算其中显示的项目。我的回收站工作得很好。我的最终目标是在我的recyclerview为空时更改布局。我试过用 getItemCount , onDataChanged 以及 ObservableSnashotArray . 我读了很多解答，但我的 getItemcount 每次返回0。
这是我的适配器：

public class ArticleAdapter extends FirestoreRecyclerAdapter<Article, ArticleAdapter.ArticleHolder> {
private ArticleAdapter.OnItemClickListener listener;
private FirestoreRecyclerOptions<Article> options;
private ObservableSnapshotArray<Article> mSnapshots;

public ArticleAdapter(FirestoreRecyclerOptions<Article> options) {
    super(options);
    this.options = options;
    mSnapshots = options.getSnapshots();

}

@Override
protected void onBindViewHolder(final ArticleHolder holder, int position, Article model) {

    holder.textViewTitle.setText(model.getTitle());
    holder.textViewDescription.setText(model.getDescription());
    holder.textViewPrice.setText("(" + model.getPrice() + "$)");
}

@NonNull
@Override
public ObservableSnapshotArray<Article> getSnapshots() {
    return mSnapshots;
}

@Override
public int getItemCount() {
    final int count = options.getSnapshots() != null
            ? options.getSnapshots().size() : 0;
    return count;
}

@NonNull
@Override
public ArticleHolder onCreateViewHolder(ViewGroup parent, int viewType) {

    View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.article_item,
            parent, false);
    return new ArticleAdapter.ArticleHolder(v);

}

class ArticleHolder extends RecyclerView.ViewHolder {
    public TextView textViewTitle;
    public TextView textViewDescription;
    public TextView textViewPrice;
    public TextView textViewQuantity;
    public TextView textViewEmpty;
    public Button mbuttonPlusArticle;
    public Button mbuttonminusArticle;
    CardView cardView;

    public ArticleHolder(final View itemView) {
        super(itemView);
        textViewTitle = itemView.findViewById(R.id.text_view_articletitle);
        textViewDescription = itemView.findViewById(R.id.text_view_articledescription);
        textViewPrice = itemView.findViewById(R.id.text_view_articleprice);
        textViewQuantity = itemView.findViewById(R.id.text_view_articlequantity);
        cardView = itemView.findViewById(R.id.mCardView);
        mbuttonPlusArticle = itemView.findViewById(R.id.bn_articleplus);
        mbuttonminusArticle = itemView.findViewById(R.id.bn_articleminus);
        textViewEmpty = itemView.findViewById(R.id.text_view_empty);

                  itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (listener != null) {
                    int position = getAdapterPosition();
                    if (position != RecyclerView.NO_POSITION && listener != null) {
                        listener.onItemClick(getSnapshots().getSnapshot(position), position);
                    }
                }
            }
        });

        cardView.setOnCreateContextMenuListener(new View.OnCreateContextMenuListener() {
            @Override
            public void onCreateContextMenu(ContextMenu contextMenu, View view, ContextMenu.ContextMenuInfo contextMenuInfo) {

                if (listener != null) {
                    int position = getAdapterPosition();
                    contextMenu.setHeaderTitle("Choisir votre Options");
                    contextMenu.add(getAdapterPosition(), 121, 0, "Modifier");
                    contextMenu.add(getAdapterPosition(), 122, 1, "Supprimer");
                    if (position != RecyclerView.NO_POSITION && listener != null) {
                        listener.onCardViewClick(getSnapshots().getSnapshot(position), position);
                    }
                }

            }
        });

        mbuttonPlusArticle.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (listener != null) {
                    int position = getAdapterPosition();
                    if (position != RecyclerView.NO_POSITION && listener != null) {
                        int count = Integer.parseInt(String.valueOf(textViewQuantity.getText()));
                        count++;
                        textViewQuantity.setText("" + count);
                        int quantity = Integer.parseInt(String.valueOf(textViewQuantity.getText()));
                        listener.onItemClickPlus(getSnapshots().getSnapshot(position), position, quantity);
                    }
                }
            }
        });

        mbuttonminusArticle.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (listener != null) {
                    int position = getAdapterPosition();
                    if (position != RecyclerView.NO_POSITION && listener != null) {
                        int count = Integer.parseInt(String.valueOf(textViewQuantity.getText()));
                        if (count == 0) {
                        } else {
                            count--;
                        }
                        textViewQuantity.setText("" + count);
                        int quantity = Integer.parseInt(String.valueOf(textViewQuantity.getText()));
                        listener.onItemClickMinus(getSnapshots().getSnapshot(position), position, quantity);
                    }
                }
            }
        });
    }

}

还有我的片段：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment

    String collectionid = getActivity().getIntent().getStringExtra("EVENT_ID");

    View view = inflater.inflate(R.layout.fragment_article, container, false);
    textViewResultatCommande = view.findViewById(R.id.text_view_resultatcommande);
    textViewEmpty = view.findViewById(R.id.text_view_empty);
    bn_commande = view.findViewById(R.id.bn_Valider_commande);
    bn_commande.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            open_dialog(view);
        }
    });
    setUpRecyclerview(view);
    setUpListView(view);
    dialog = new Dialog(getActivity());
    return view;
}

private void setUpRecyclerview(final View view) {
    String collectionid = getActivity().getIntent().getStringExtra("EVENT_ID");
    final Query query = articlelistref
            .document(collectionid)
            .collection("Articlebook")
            .orderBy("title", Query.Direction.DESCENDING);

    FirestoreRecyclerOptions<Article> options = new FirestoreRecyclerOptions.Builder<Article>()
            .setQuery(query, Article.class)
            .build();

    adapter = new ArticleAdapter(options);

    final RecyclerView recyclerView = view.findViewById(R.id.recycler_view_historique);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(view.getContext()));
    recyclerView.setAdapter(adapter);
    adapter.startListening();

    Toast.makeText(getActivity(), "Nombre 2 :" +adapter.getItemCount(), Toast.LENGTH_SHORT).show();

你能帮助我吗？谢谢您