Get data from firebase in fragment with recycleview

Question

I'm trying to get data from firebase in RecycleView in Fragment, but when I do this it doesn't show any thing, but when I but recycleview in activity , it work, so what's the problem ?

• I have read many questions like my own but I didn't find a solution, why the recycleview doesn't show any thing, and when I put it in activity it work without problem?

Fragment

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        final View view = inflater.inflate(R.layout.tab1, container, false);


        final FragmentActivity c = getActivity();
        rv = view.findViewById(R.id.rv);
        rv.setLayoutManager(new LinearLayoutManager(c));


        db= FirebaseDatabase.getInstance().getReference();
        helper=new FirebaseHelper(db);

        adapter=new MyAdapter(c,helper.retrieve());
        rv.setAdapter(adapter);

        Toast.makeText(c,"done",Toast.LENGTH_LONG).show();

        return inflater.inflate(R.layout.tab1, container, false);

        }

}

FirbaseHelper

public class FirebaseHelper {

    DatabaseReference db;
    Boolean saved=null;
    ArrayList<Spacecraft> spacecrafts=new ArrayList<>();

    public FirebaseHelper(DatabaseReference db) {
        this.db = db;
    }

    //WRITE IF NOT NULL
    public Boolean save(Spacecraft spacecraft)
    {
        if(spacecraft==null)
        {
            saved=false;
        }else
        {
            try
            {
                db.child("Spacecraft").push().setValue(spacecraft);
                saved=true;

            }catch (DatabaseException e)
            {
                e.printStackTrace();
                saved=false;
            }
        }

        return saved;
    }

    //IMPLEMENT FETCH DATA AND FILL ARRAYLIST
    private void fetchData(DataSnapshot dataSnapshot)
    {
        spacecrafts.clear();

        for (DataSnapshot ds : dataSnapshot.getChildren())
        {
            Spacecraft spacecraft=ds.getValue(Spacecraft.class);
            spacecrafts.add(spacecraft);
        }
    }

    //READ THEN RETURN ARRAYLIST
    public ArrayList<Spacecraft> retrieve() {
        db.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                fetchData(dataSnapshot);




            }

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

            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

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

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
        return spacecrafts;
    }
}

Adabter

public class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {

    Context c;
    ArrayList<Spacecraft> spacecrafts;

    public MyAdapter(Context c, ArrayList<Spacecraft> spacecrafts) {
        this.c = c;
        this.spacecrafts = spacecrafts;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v=LayoutInflater.from(c).inflate(R.layout.model,parent,false);
        return new MyViewHolder(v);
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        final  Spacecraft s=spacecrafts.get(position);

        holder.nameTxt.setText(s.getName());
        holder.propTxt.setText(s.getPropellant());
        holder.descTxt.setText(s.getDescription());

        holder.setItemClickListener(new ItemClickListener() {
            @Override
            public void onItemClick(int pos) {
                //OPEN DETAI ACTIVITY
                openDetailActivity(s.getName(),s.getDescription(),s.getPropellant());
            }
        });
    }

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

    //OPEN DETAIL ACTIVITY
    private void openDetailActivity(String...details)
    {
        Intent i=new Intent(c,DetailActivity.class);

        i.putExtra("NAME_KEY",details[0]);
        i.putExtra("DESC_KEY",details[1]);
        i.putExtra("PROP_KEY",details[2]);

        c.startActivity(i);
    }
}

Spacecraft

public class Spacecraft {

    String name,propellant,description;

    public Spacecraft() {
    }

    public String getName() {
        return name;
    }

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

    public String getPropellant() {
        return propellant;
    }

    public void setPropellant(String propellant) {
        this.propellant = propellant;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}

Answer 1

Add one more line of code in your fragment after setting adapter to recycler view.

adapter.notifyDataSetChanged();

You forget to notify the adapter after getting data.

adapter=new MyAdapter(c,helper.retrieve());
rv.setAdapter(adapter);
adapter.notifyDataSetChanged();