Android Firebase Recyclerview 适配器未填充数据 - mSnapshots 为 0

Question

Hi I am not sure where I am going wrong with my FirebaseRecycler - I am not getting errors in either the run or logcat. I am just getting a blank activity and the debugger output shows that the FirebaseRecyclerOptions mSnapshot array is size 0. Any help would be great!

Here is how the firebase data looks: firebase data

logcat output: logcat image

debuger output: debug image (breakpoint was set at last line of MainActivity onCreate method)

MainActivity:

public class MainActivity extends AppCompatActivity {

RecyclerView recview;
Adapter adapter;

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

    recview = (RecyclerView)findViewById(R.id.recview);


    FirebaseRecyclerOptions<Podcast> options =
            new FirebaseRecyclerOptions.Builder<Podcast>()
            .setQuery(FirebaseDatabase.getInstance().getReference().child("top10"),Podcast.class)
            .build();

    adapter = new Adapter(options);
    GridLayoutManager gridLayoutManager = new GridLayoutManager(this,1,GridLayoutManager.VERTICAL,false);
    recview.setLayoutManager(gridLayoutManager);
    recview.setAdapter(adapter);
}

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

@Override
protected void onStop() {
    super.onStop();
    adapter.stopListening();
}}

Here is the model class I am using called Podcasts:

public class Podcast {

private String rss;
private String title;
private Integer order;

public Podcast(){

}

public Podcast(String url, String title, Integer order){
    this.rss = url;
    this.title = title;
    this.order = order;
}

public String getTitle(){
    return title;
}
public String getRss(){
    return rss;
}
public Integer getOrder(){
    return order;
}
public void setTitle(String title) {this.title = title;}
public void setRss(String rss){this.rss = rss;}
public void setOrder(Integer order){this.order = order;}}

Here is the Adapter class:

public class Adapter extends FirebaseRecyclerAdapter<Podcast,Adapter.myviewholder> {

LayoutInflater inflater;

//constructor
public Adapter(@NonNull FirebaseRecyclerOptions<Podcast> options){
    super(options);
    //inherits titles and url from the Podcast class
}

@Override
protected void onBindViewHolder(@NonNull myviewholder holder, int position, @NonNull Podcast model) {
    holder.name.setText(model.getTitle());      //model is the podcast object
    holder.url.setText(model.getRss());
    holder.order.setText(model.getOrder());
    //image with picasso next
}

@NonNull
@Override
public myviewholder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = inflater.inflate(R.layout.custom_grid_layout,parent,false);
    return new myviewholder(view);
}

public static class myviewholder extends RecyclerView.ViewHolder
{
    TextView name;
    TextView url;
    TextView order;

    public myviewholder(@NonNull View itemView)
    {
        super(itemView);
        name = (TextView)itemView.findViewById(R.id.textView2);
        url = (TextView)itemView.findViewById(R.id.url);
        order = (TextView)itemView.findViewById(R.id.order);

    }
}}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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"
    tools:context=".MainActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:layout_editor_absoluteX="306dp"
        tools:layout_editor_absoluteY="397dp" />
</androidx.constraintlayout.widget.ConstraintLayout>

custom_gridview_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    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="wrap_content"
    android:layout_height="wrap_content">

    <androidx.cardview.widget.CardView
        android:id="@+id/cardView"
        android:layout_width="wrap_content"
        android:layout_height="159dp"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="52dp"
        app:cardPreventCornerOverlap="true"
        app:contentPadding="10dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="328dp"
            android:layout_height="127dp">

            <TextView
                android:id="@+id/textView2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="43dp"
                android:layout_marginLeft="43dp"
                android:layout_marginEnd="44dp"
                android:layout_marginRight="44dp"
                android:layout_marginBottom="16dp"
                android:paddingRight="10dp"
                android:text="TextView"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent" />

            <TextView
                android:id="@+id/url"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="132dp"
                android:layout_marginLeft="132dp"
                android:layout_marginEnd="138dp"
                android:layout_marginRight="138dp"
                android:layout_marginBottom="13dp"
                android:text="TextView"
                app:layout_constraintBottom_toTopOf="@+id/textView2"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent" />

            <TextView
                android:id="@+id/order"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="130dp"
                android:layout_marginLeft="130dp"
                android:layout_marginTop="30dp"
                android:layout_marginEnd="140dp"
                android:layout_marginRight="140dp"
                android:text="TextView"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

        </androidx.constraintlayout.widget.ConstraintLayout>
    </androidx.cardview.widget.CardView>

</RelativeLayout>

Answer 1

In your database when you getReference it will get "testapi-232613-defa..." and calling child will bring the key "1wertHC2Qy..." and not "top10" that is why its unable to get any data

Answer 2

Hi it turns out that the issue was related to the Adapter needing a typecast for the Inflater:

old: view = inflater.inflate(R.layout.custom_grid_layout,parent,false);

new: View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.custom_grid_layout,parent,false)

Also I changed the database reference to:

DatabaseReference myRef = database.getReferenceFromUrl("https://testapi-232613-default-rtdb.firebaseio.com/1wertHC2QykkMJPdc6aPgV1pasPB8mFpkOyuuCRk1kE0/top10");

and used that as the args for the setQuery() function

Answer 3

You should change the database preference to

DatabaseReference myRef = database.getReferenceFromUrl("https://testapi-232613-default-rtdb.firebaseio.com/1wertHC2QykkMJPdc6aPgV1pasPB8mFpkOyuuCRk1kE0/top10");

Do check it out.