FirestoreAdapter not working to populate a Recycle

问题:

I'm a rookie with Android and decided to use Cloud Firestore as my db and a RecyclerView for populating a list in my MainActivity. I thought using Firebase-UI for Firestore would be super easy, but I can't figure out why nothing is populating in my RecyclerView. For reference, here is the Firebase UI page and here is the example code that I based my app off of. All I'm trying to do is populate a list of "Courses" (Course.java not displayed below since it's just a simple POJO with name, date, etc.) the user has saved in the db.

MainActivity:

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.PopupMenu;
import android.support.v7.widget.RecyclerView;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;

import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.FirebaseFirestoreException;
import com.google.firebase.firestore.Query;
import com.lorin.deadlineschmedline.R;
import com.lorin.deadlineschmedline.adapters.CourseAdapter;

import butterknife.BindView;
import butterknife.ButterKnife;

public class MainActivity extends AppCompatActivity
        implements CourseAdapter.OnCourseSelectedListener,
        PopupMenu.OnMenuItemClickListener {

private FirebaseFirestore mFirestore;
private Query mQuery;
private FirebaseUser mCurrentUser;

private RecyclerView.Adapter mAdapter;

private static final String TAG = "MainActivity";
private static final int RC_SIGN_IN = 9001;
private static final int LIMIT = 50;

@BindView(R.id.rv_course_item_list)
RecyclerView mCourseRecyvlerView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ButterKnife.bind(this);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            showPopup(view);
        }
    });

    // Enable Firestore logging
    FirebaseFirestore.setLoggingEnabled(true);

    // Firestore
    mFirestore = FirebaseFirestore.getInstance();
    mQuery = mFirestore.collection("courses").whereEqualTo("name", true).limit(LIMIT);
    mAdapter = new CourseAdapter(mQuery, this) {
        @Override
        protected void onDataChanged() {
            // Show/hide content if the query returns empty.
            if (getItemCount() == 0) {
                mCourseRecyvlerView.setVisibility(View.VISIBLE);
                //mEmptyView.setVisibility(View.VISIBLE);
            } else {
                mCourseRecyvlerView.setVisibility(View.VISIBLE);
                //mEmptyView.setVisibility(View.GONE);
            }
        }

        @Override
        protected void onError(FirebaseFirestoreException e) {
            // Show a snackbar on errors
            Snackbar.make(findViewById(android.R.id.content),
                    "Error: check logs for info.", Snackbar.LENGTH_LONG).show();
        }
    };

    mCourseRecyvlerView.setLayoutManager(new LinearLayoutManager(this));
    mCourseRecyvlerView.setAdapter(mAdapter);
}

private void showPopup(View v) {
    PopupMenu popup = new PopupMenu(this, v);
    MenuInflater inflater = popup.getMenuInflater();
    inflater.inflate(R.menu.add_component_menu, popup.getMenu());
    popup.setOnMenuItemClickListener(this);
    popup.show();
}

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

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

    if (mAdapter != null) {
        mAdapter.stopListening();
    }
}

@Override
public boolean onMenuItemClick(MenuItem item) {
    switch(item.getItemId()) {
        case R.id.add_course:
            startActivity(new Intent(MainActivity.this, AddCourseActivity.class));
            return true;
        case R.id.add_course_component:
            startActivity(new Intent(MainActivity.this, AddCourseComponentActivity.class));
            return true;
        default:
            return true;
    }
}

@Override
public void onCourseSelected(DocumentSnapshot restaurant) {
    // Go to the details page for the selected activity
    Intent intent = new Intent(this, AddCourseActivity.class);
    startActivity(intent);

    //overridePendingTransition(R.anim.slide_in_from_right, R.anim.slide_out_to_left);
}

}

I've tried stepping through the MainActivity with the debugger, but I can't make heads or tails of what I'm getting back from Firestore when I Query the db (which may be the issue). Any thoughts and feedback would be greatly appreciated!

回答1:

In order to make it work, you need to start listening for changes and for that, please call startListening() method on your adapter object inside the onStart() method from your MainActivity class like this:

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

And to stop listening, please use the following code:

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

    if (mAdapter != null) {
        mAdapter.stopListening();
    }
}

回答2:

It turned out to be an issue with the Firestore Query. Previously, I had used:

mQuery = mFirestore.collection("courses").whereEqualTo("name", true).limit(LIMIT);

However, it appears that you must use the orderBy() method when making a Firestore Query. Using the following did the trick:

mQuery = mFirestore.collection("courses").orderBy("name").limit(LIMIT);

Now my data is showing up in the RecyclerView as anticipated.