无法让 FirestoreRecyclerAdapter 显示项目

Posted 2023-02-22

【中文标题】无法让 FirestoreRecyclerAdapter 显示项目

【英文标题】：Can't get FirestoreRecyclerAdapter to show items

【发布时间】：2018-10-11 16:15:06

【问题描述】：

我正在更新我的应用以使用 Firebase 的 Firestore 数据库。我正在努力让应用程序显示从数据库中检索到的数据。数据检索正常，但不显示。通过设置断点，我已经确定 ViewHolder 在任何时候都没有绑定到适配器。

数据显示在片段中。 Fragment 布局是（我已经去掉了不相关的东西，比如填充、大小等）：

<android.support.constraint.ConstraintLayout
    android:id="@+id/layout_charts_list"
    tools:context="apppath.fragments.ChartListFragment">

    <TextView
        android:id="@+id/loading_list"
        android:text="@string/loading_my_charts" />

    <TextView
        android:id="@+id/empty_list"
        android:text="@string/my_charts_empty"
        android:visibility="gone"/>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/charts_list" />

</android.support.constraint.ConstraintLayout>

片段代码本身是：

public abstract class ChartListFragment extends Fragment 

    private FirebaseFirestore mDatabaseRef;
    private FirestoreRecyclerAdapter<Chart, ChartViewHolder> mAdapter;
    private Query mChartsQuery;
    private RecyclerView mRecycler;

    public ChartListFragment() 

    @Override
    public View onCreateView(LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) 
        super.onCreateView(inflater, container, savedInstanceState);

        View rootView = inflater.inflate(
                R.layout.fragment_charts_list, container, false);

        mRecycler = rootView.findViewById(R.id.charts_list);
        mRecycler.setHasFixedSize(true);

        // Set up Layout Manager, and set Recycler View to use it
        LinearLayoutManager mManager = new LinearLayoutManager(getActivity());
        mManager.setReverseLayout(true);
        mManager.setStackFromEnd(true);
        mRecycler.setLayoutManager(mManager);

        // Connect to the database, and get the appropriate query (as set in the actual fragment)
        mDatabaseRef = FirebaseFirestore.getInstance();
        mChartsQuery = getQuery(mDatabaseRef);

        // Set up Recycler Adapter
        FirestoreRecyclerOptions<Chart> recyclerOptions = new FirestoreRecyclerOptions.Builder<Chart>()
                .setQuery(mChartsQuery, Chart.class)
                .build();

        mAdapter = new ChartListAdapter(recyclerOptions);

        // Use Recycler Adapter in RecyclerView
        mRecycler.setAdapter(mAdapter);

        return rootView;
    

    @Override
    public void onActivityCreated(Bundle savedInstanceState) 
        super.onActivityCreated(savedInstanceState);

        // Add listener to charts collection, and deal with any changes by re-showing the list
        mChartsQuery.addSnapshotListener(new EventListener<QuerySnapshot>() 
            @Override
            public void onEvent(@Nullable QuerySnapshot queryDocumentSnapshots,
                                @Nullable FirebaseFirestoreException e) 

                if (queryDocumentSnapshots != null && queryDocumentSnapshots.isEmpty()) 
                    ((MainActivity) getActivity()).setPage(1);
                    mRecycler.setVisibility(View.GONE);
                else 
                    mRecycler.setVisibility(View.VISIBLE);
                

            
        );
    


    // HELPER FUNCTIONS

    public abstract Query getQuery(FirebaseFirestore databaseReference);

ChartListAdapter如下：

public class ChartListAdapter
        extends FirestoreRecyclerAdapter<Chart, ChartViewHolder> 

    public ChartListAdapter(FirestoreRecyclerOptions recyclerOptions) 
        super(recyclerOptions);

    

    @Override
    protected void onBindViewHolder(ChartViewHolder holder, int position, Chart model) 
        holder.setChartName(model.getName());

        // Bind Chart to ViewHolder
        holder.bindToChart(model);
    

    @Override
    public ChartViewHolder onCreateViewHolder(ViewGroup parent, int viewType) 
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_chart, parent, false);

        return new ChartViewHolder(view);
    

ChartViewHolder：

public class ChartViewHolder extends RecyclerView.ViewHolder 

    private TextView chartNameView;
    private String chartKey;

    public ChartViewHolder(View itemView) 
        super(itemView);

        chartNameView = itemView.findViewById(R.id.chart_name);
    

    public void setChartName(String chartName) 
        chartNameView.setText(chartName);
    

    public void bindToChart(Chart chart) 
        chartKey = chart.getKey();
        chartNameView.setText(chart.getName());
    

    public String getChartKey() 
        return chartKey;
    

调用了 ChartListAdapter 构造函数，但从不调用 onBindViewHolder 和 onCreateViewHolder，并且从不访问 ChartViewHolder。我错过了一行代码吗？或者这样做完全错误？我对 Adapters 和 RecyclerViews 不是很熟悉，所以我发现很难把它们放在一起。

【参考方案1】：

对于那些从 Google 来到这里的人，请在选项上设置生命周期所有者，以便自动调用开始/停止侦听。

FirestoreRecyclerOptions<Chart> recyclerOptions = FirestoreRecyclerOptions.Builder<Chart>()
            .setQuery(mChartsQuery, Chart.class)
            .setLifecycleOwner(this)
            .build();

【参考方案2】：

您需要添加以下内容，开始监听数据，调用startListening() 方法。您可能想在您的 onStart() 方法中调用它。在调用 startListening() 之前，请确保您已完成读取数据所需的任何身份验证，否则您的查询将失败：

@Override
protected void onStart() 
super.onStart();
adapter.startListening();

更多信息在这里：

https://github.com/firebase/FirebaseUI-Android/tree/master/firestore