FirestoreRecyclerAdapter-如何知道何时检索数据？

Question

I'm retrieving data using a FirestoreRecyclerAdapter , and, on completion, I need to check whether any items have been retrieved or not. I can't figure out how to do this.

I'm calling it from a class called FragmentChartsList , shown below. This should set up the adapter initially, with "name" as the value for mOrder . Later, the Activity which contains this Fragment can call setOrderField() with a different value of mOrder , which the user has selected from a Spinner.

Each time setOrderField() is called, a new adapter instance is created and attached to the recyclerView. At this point I need to check whether the new version of the adapter contains any data, and either show a "no Charts found" message, or show the Charts which were retrieved (obviously if the list is just being sorted, then the number of items remains the same, but I'm going to be expanding this to allow the user to filter the Charts by different criteria, so the number of Charts returned will change).

Currently, setOrderField() calls refreshViewOnNewData() , which should find out how many Charts are being shown; if it's 0, it should show the "no Charts found" message, and if it's >0 it should show the RecyclerView containing the Charts.

At the moment, I'm always getting a value of 0 when I try to count the Charts. I suspect it's because the adapter hasn't finished retrieving them from the database yet, but I can't find anything that allows me to add some kind of " onComplete " listener so that I know it's finished.

Can anyone suggest how I can achieve this?

public abstract class FragmentChartsList extends Fragment {

    private FirebaseFirestore mDatabaseRef;
    private ChartListAdapter mAdapter;
    private Query mChartsQuery;
    private RecyclerView mRecycler;
    private String mOrder = "name";

    private TextView mLoadingList, mEmptyList;

    public FragmentChartsList() {}

    @Override
    public View onCreateView(@NonNull 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);

        mLoadingList = rootView.findViewById(R.id.loading_list);
        mEmptyList = rootView.findViewById(R.id.empty_list);

        // 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
        mDatabaseRef = FirebaseFirestore.getInstance();

        setOrderField(mOrder); // Initialised to "name"

        return rootView;
    }

    @Override
    public void onStart() {
        super.onStart();
        mAdapter.startListening();
    }

    @Override
    public void onStop() {
        super.onStop();
        mAdapter.stopListening();
    }

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

        mAdapter.stopListening();
    }


    // HELPER FUNCTIONS

    public void setOrderField(String order) {

        mOrder = order;
        mChartsQuery = getQuery(mDatabaseRef, mOrder);

        // Update recycler options
        FirestoreRecyclerOptions<Chart> recyclerOptions = new FirestoreRecyclerOptions.Builder<Chart>()
                .setQuery(mChartsQuery, Chart.class)
                .build();

        mAdapter = new ChartListAdapter(recyclerOptions, getActivity());
        mAdapter.startListening();

        mRecycler.swapAdapter(mAdapter, true);

        refreshViewOnNewData();

    }

    private void refreshViewOnNewData() {

        // Hide "loading" text
        mLoadingList.setVisibility(View.GONE);

        // Check number of charts being shown
        //if (mAdapter != null && (mAdapter.getCount() > 0)) {
            // If > 0, show Charts
            mEmptyList.setVisibility(View.GONE);
            mRecycler.setVisibility(View.VISIBLE);

        } else {
            // If number of Charts = 0
            //    show "no charts"
            mEmptyList.setVisibility(View.VISIBLE);
            mRecycler.setVisibility(View.GONE);
        }

    }

}

The adapter class looks like this:

public class ChartListAdapter extends FirestoreRecyclerAdapter<Chart, ChartViewHolder> {

    private Activity mActivity;
    private int mCount;

    public ChartListAdapter(FirestoreRecyclerOptions<Chart> recyclerOptions, Activity activity) {
        super(recyclerOptions);

        mActivity = activity;

    }

    @Override
    protected void onBindViewHolder(@NonNull ChartViewHolder holder, int position, @NonNull Chart model) {

        final String chartKey = this.getSnapshots().getSnapshot(position).getId();

        model.setKey(chartKey);

        // Set click listener for the chart
        // On click, the user can view the chart
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(mActivity, ActivityViewChart.class);
                intent.putExtra("ChartKey", chartKey);
                mActivity.startActivity(intent);
            }
        });

        // Implement long-click menu
        mActivity.registerForContextMenu(holder.itemView);

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

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

        return new ChartViewHolder(view);
    }

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

        mCount = getItemCount();

    }

    public int getCount() {
        return mCount;
    }

}

Answer 1

Figured this out... I needed to set a listener on the query instead.

So, instead of having the call to refreshViewOnNewData from setOrder above, I now have:

    mChartsQuery.addSnapshotListener(new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(@Nullable QuerySnapshot queryDocumentSnapshots, @Nullable FirebaseFirestoreException e) {


            if (queryDocumentSnapshots != null) {

                mLoadingList.setVisibility(View.GONE);

                if(queryDocumentSnapshots.size() > 0) {
                    mEmptyList.setVisibility(View.GONE);
                    mRecycler.setVisibility(View.VISIBLE);
                }else {
                    mEmptyList.setVisibility(View.VISIBLE);
                    mRecycler.setVisibility(View.GONE);
                }
            }

        }
    });

}

Also removed mCount from the adapter class, along with getCount and onDataChanged