java.util.ArrayList.size()' on a null object reference

Question

I want to pull data from my Firebase database. My table name is "cardornek". And I set the permissions for read/write.

But I get this "java.util.ArrayList.size()' on a null object reference" error. Any idea?

RecyclerViewAdapter.java

public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> {

private ArrayList<String> values=null;
RecyclerViewAdapter(ArrayList<String> values) {
    this.values = values;
}
@Override
public RecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_view_item,parent,false));
}


@Override
public void onBindViewHolder(RecyclerViewAdapter.ViewHolder holder, int position)
{
    holder.name.setText(values.get(position));
}

@Override
public int getItemCount() {
    return values.size();
}

public class ViewHolder extends RecyclerView.ViewHolder
{
    private TextView name;
    ViewHolder(View itemView) {
        super(itemView);
        name = (TextView) itemView.findViewById(R.id.list_item_text);
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    new GetDataFromFirebase().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);

    // Read from the database
    FirebaseDatabase database = FirebaseDatabase.getInstance();
    DatabaseReference myRef = database.getReference("cardornek");

    myRef.addValueEventListener(new ValueEventListener() {


        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            ArrayList<String> values = (ArrayList<String>) dataSnapshot.getValue();
            recyclerView.setAdapter(new RecyclerViewAdapter(values));
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            System.out.println("Failed to read value." + databaseError.toException());
        }
    });

dataSnapshot.getValue() returns null so you pass null into the constructur of your RecyclerViewAdapter and when android calls getItemCount() you get a NullPointerException — larsgrefer
– larsgrefer, Commented Dec 23, 2016 at 20:44
check the following example: github.com/firebase/quickstart-android/tree/master/database/app/… — wake-0
– wake-0, Commented Dec 23, 2016 at 20:50
I'm checking this example github.com/jefrisingh/… cause I don't use Auth process. — Yunus Haznedar
– Yunus Haznedar, Commented Dec 23, 2016 at 20:59

Lajos Arpad · Accepted Answer · 2016-12-23 21:12:47Z

12

Your problem is that (ArrayList<String>) dataSnapshot.getValue() is sometimes null and after you store values, the exception is thrown in getItemCount. If you are ok with returning 0 as size when values is null, then the solution is

@Override
public int getItemCount() {
    return (values == null) ? 0 : values.size();
}

However, you might want to find out why dataSnapshot.getValue can return null. Maybe that's the real problem and the NullPointerException is just the symptom.

answered Dec 23, 2016 at 21:12

Lajos Arpad

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3 Comments

Yunus Haznedar Over a year ago

Yes! Thanks it is working now. But there is no data showing up on cardview. I should check my database I think. Thanks mate!

Matt Over a year ago

What would this do?

Lajos Arpad Over a year ago

@Matt it returns 0 of values is null. If not, it returns the size of values. This is a neat way to avoid null pointer exception.

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