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I am trying to retrieve data into a RecyclerView from Firebase Database but am experiencing this error java.lang.NullPointerException: Attempt to invoke virtual method. 'com.google.firebase.database.DatabaseReference com.google.firebase.database.DatabaseReference.child(java.lang.String)' on a null object reference

Below is my main activity class .

    package oerrride.we.huzykamz.testingappfirebase;

    import android.app.Dialog;
    import android.content.Context;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.support.v7.widget.LinearLayoutManager;
    import android.support.v7.widget.RecyclerView;
    import android.view.View;
    import android.widget.Button;

    import com.google.android.gms.common.GoogleApiAvailability;
    import com.google.android.gms.tasks.Task;
    import com.google.firebase.database.ChildEventListener;
    import com.google.firebase.database.DataSnapshot;
    import com.google.firebase.database.DatabaseError;
    import com.google.firebase.database.DatabaseReference;
    import com.google.firebase.database.FirebaseDatabase;
    import com.google.firebase.database.ValueEventListener;

    import java.util.ArrayList;
    import java.util.List;


    public class MainActivity extends AppCompatActivity {

        private Button but;
        private DatabaseReference mRef;
        private MyAdapter adapter;
        public RecyclerView recyclerView;

        public List<ModelClass> movies_;
        public Context c;
        private LinearLayoutManager linearLayoutManager;

        private DatabaseReference mMovieRef =mRef.child("Name");

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            movies_ = new ArrayList<ModelClass>();

            recyclerView =(RecyclerView) findViewById(R.id.recyclerview);

            linearLayoutManager = new LinearLayoutManager(this);
            recyclerView.setLayoutManager(linearLayoutManager);
            recyclerView.setHasFixedSize(true);
            mRef =  FirebaseDatabase.getInstance().getReferenceFromUrl("xxxxxxxxxxxxxxxxxxxxxx");


            mRef.addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    LoadData(dataSnapshot);
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s) {
                    LoadData(dataSnapshot);
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });




        }



        public void LoadData (DataSnapshot dataSnapshot){
            for(DataSnapshot singlesnapshot :dataSnapshot.getChildren()){
              String taskTitle =singlesnapshot.getValue(String.class);

                movies_.add(new ModelClass(taskTitle));

                adapter = new MyAdapter(MainActivity.this, movies_);
                recyclerView.setAdapter(adapter);



            }

        }

    }


And this is my Adapter class .







public class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {




 protected   Context c;
    List<ModelClass> movies;

public MyAdapter(Context c, List<ModelClass> movies) {
    this.c = c;
    this.movies = movies;
}

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

    View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_activity,parent,false);
    MyViewHolder holder = new MyViewHolder(v);
    return holder;
}

@Override
public void onBindViewHolder(MyViewHolder holder, int position) {

    holder.name.setText(movies.get(position).getName());
  // PicassoClient.downloadImage(c,movies.get(position).getUrl(),holder.img);

}

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

}

Below is my Console of Firebase database

Firebase Console data am trying to fetch

Lutaaya Huzaifah Idris
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3 Answers3

9
private DatabaseReference mMovieRef =mRef.child("Name");

mRef is not created yet so It is null and will throw NullPointerException

Solution:

Change your declaration to:

private DatabaseReference mMovieRef;

and assign value to it after you created mRef

mRef =  FirebaseDatabase.getInstance().getReferenceFromUrl("xxxxxxxxxxxxxxxxxxxxxx");
mMovieRef = mRef.child("Name");
pr0gramist
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  • Yeah the that error has changed thanks , but am experiecing another one @PoprostyRonin , it's `com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.HashMap to String` – Lutaaya Huzaifah Idris Sep 17 '16 at 12:30
  • Ooooh yeah i have got the reason for that Error , my data formatting was poor , i have adjusted it now its working perfect . :) @ @PoprostyRonin – Lutaaya Huzaifah Idris Sep 17 '16 at 12:38
0

probably DatabaseReference is not intialized :try using:

     private DatabaseReference mMovieRef =new DatabaseReference()
               mRef.child("Name");

or here it can be:

     private DatabaseReference mMovieRef =FirebaseDatabase.getInstance().getReferenceFromUrl("xxxxxxxxxxxxxxxxxxxxxx");
mRef.child("Name");

instead of

   private DatabaseReference mMovieRef =mRef.child("Name");
DevKRos
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0

You don't need to initialize or declare your DatabaseReference outside the main. I mean don't declare it outside as a private variable!

DatabaseReference mMovieRef = FirebaseDatabase.getInstance().getReferenceFromUrl("xxxxxxxxxxxxxxxxxxxxxx");
mRef.child("Name");

From here you can add your listener

Shredator
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Mandy
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