使用FirestoreRecyclerAdapter和DocumentReference时，不会在RecyclerView中显示用户

Question

我正在使用Cloud Firestore。我的Firestore数据库文档名称是用户，我想在Android RecyclerView和我的活动名称MainActivity中显示所有用户，并且我使用此XML文件activity_main.xml。

在跑步时会显示空白活动。

activity_main.xml中

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="5dp"
    tools:context="com.example.anuragtiwari.recyclerdemo.MainActivity">

    <android.support.v7.widget.RecyclerView
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:id="@+id/recyclerview_list"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="7dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="7dp"
        android:layout_marginStart="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.073"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0"
        android:layout_alignParentTop="true">

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

</android.support.constraint.ConstraintLayout>

MainActivity.java

public class MainActivity extends AppCompatActivity {


    private RecyclerView mUsersList;
    private CollectionReference muser;
    private FirestoreRecyclerAdapter adapter;
    LinearLayoutManager linearLayoutManager;


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

        mUsersList = (RecyclerView) findViewById(R.id.recyclerview_list);

        mUsersList.setLayoutManager(new LinearLayoutManager(this));
        muser = FirebaseFirestore.getInstance().collection("users");
        Query query = muser;


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

        FirestoreRecyclerAdapter adapter = new FirestoreRecyclerAdapter<Users, FriendsHolder>(options)
        {

            @Override
            public FriendsHolder onCreateViewHolder(ViewGroup group, int i)
            {
                View view = LayoutInflater.from(group.getContext())
                        .inflate(R.layout.single_user, group, false);
                return new FriendsHolder(view);
            }

            @Override
            public void onError(FirebaseFirestoreException e)
            {
                Log.e("error", e.getMessage());
            }

            @Override
            protected void onBindViewHolder(FriendsHolder holder, int position, Users model) {
                holder.nameText.setText(model.getName());
                holder.emailText.setText(model.getEmail());


            }

        };
        mUsersList.setAdapter(adapter);
    }

    private class FriendsHolder extends RecyclerView.ViewHolder
    {
        View mView;
        public TextView nameText;
        public TextView emailText;

        public FriendsHolder(View itemview) {
            super(itemview);
            mView = itemview;
            nameText = (TextView) mView.findViewById(R.id.single_user_name);
            emailText = (TextView) mView.findViewById(R.id.single_user_email);

        }
    }
}

single_user.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_margin="15dp"
    android:layout_height="match_parent">



    <TextView
        android:id="@+id/single_user_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="27dp"
        android:layout_marginStart="27dp"
        android:text="Display Name"
        android:textColor="@android:color/black"
        android:textSize="18sp"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/single_user_email"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/single_user_name"
        android:layout_alignStart="@+id/single_user_name"
        android:layout_below="@+id/single_user_name"
        android:layout_marginTop="15dp"
        android:text="User Email" />
    <view
        android:layout_width="match_parent"
        android:layout_height="2dp"
        android:layout_marginTop="60dp"
        />
</RelativeLayout>

Users.java

public class Users
{
    public String name;
    public String email;

    public Users(){

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        name = name;
    }


    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        email = email;
    }

    public Users(String name, String email) {
        this.name = name;
        this.email = email;
    }
}

**App Images**