Firebase gives null value after for each loop

Question

I have a class Home in which data is extracted from Firebase using a method getDatafromFirebase()and when I Log the values in the loop it shows the value but when I add it into a list and update the adapter, the RecyclerView shows null for all the values.

public class Home extends Fragment {
    public Home() {}

    RecyclerView recyclerView;
    RecyclerView.LayoutManager layoutManager;
    private DatabaseReference reference = FirebaseDatabase.getInstance ().getReference ();
    ArrayList<FirebaseVideoDetials> list;
    FirebaseVideoDetials details;
    RecyclerViewAdapter adapter;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view  =inflater.inflate(R.layout.fragment_home, container, false);
        RelativeLayout without = view.findViewById(R.id.withoutInternet);
        RelativeLayout mainLayout = view.findViewById(R.id.mainLayout);
        recyclerView = view.findViewById(R.id.recyclerView);
        layoutManager = new LinearLayoutManager(getActivity());
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.addItemDecoration(new DividerItemDecoration(getActivity(),LinearLayoutManager.HORIZONTAL));
        details = new FirebaseVideoDetials();
        list = new ArrayList<FirebaseVideoDetials>();
        getDatafromFirebase();
        adapter = new RecyclerViewAdapter(getActivity(), list);
        recyclerView.setAdapter(adapter);
        if(!Internetcheck.checkConnection(getActivity())){
            without.setVisibility(View.VISIBLE);
            mainLayout.setVisibility(View.INVISIBLE);
        }else{
            without.setVisibility(View.INVISIBLE);
            mainLayout.setVisibility(View.VISIBLE);
        }
        return view;
    }

    public void getDatafromFirebase(){
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                DataSnapshot Videoreference = dataSnapshot.child("Videos");
                for (DataSnapshot videoschild : Videoreference.getChildren()){
                    DataSnapshot description = videoschild.child("Description");
                    DataSnapshot duration = videoschild.child("Duration");
                    DataSnapshot title = videoschild.child("Title");
                    DataSnapshot thumbnail = videoschild.child("Thumbnail");
                    details.setDescription(String.valueOf(description.getValue()));
                    details.setDuration(String.valueOf(duration.getValue()));
                    details.setTitle(String.valueOf(title.getValue()));
                    details.setThumbnail(String.valueOf(thumbnail.getValue()));
                    Log.e("details",details.description);
                    list.add(details);
                }
                Log.e("Size",list.get(0).description);
                adapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                Toast.makeText(getActivity(), databaseError.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
    }
}

Answer 1

I solved it by calling the add function of Listview in a separate function:

public void getDatafromFirebase(){
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                list.clear();
                DataSnapshot Videoreference = dataSnapshot.child("Videos");
                for (DataSnapshot videoschild : Videoreference.getChildren()){
                    DataSnapshot description = videoschild.child("Description");
                    DataSnapshot duration = videoschild.child("Duration");
                    DataSnapshot title = videoschild.child("Title");
                    DataSnapshot thumbnail = videoschild.child("Thumbnail");
                    DataSnapshot date = videoschild.child("Date");
                    DataSnapshot time = videoschild.child("Time");
                    updatelist(description.getValue(String.class),
                            title.getValue(String.class),
                            String.valueOf(duration.getValue()),
                            thumbnail.getValue(String.class),
                            String.valueOf(date.getValue()),
                            String.valueOf(time.getValue()));
                }
                adapter.notifyDataSetChanged();
                progressbar.setVisibility(View.GONE);

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                Toast.makeText(getActivity(), databaseError.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
    }

    public void updatelist(String desc,String title,String duration,String thumbnail,String Date,String time){
        FirebaseVideoDetials details = new FirebaseVideoDetials();
        details.setDescription(desc);
        details.setDuration(duration);
        details.setTitle(title);
        details.setThumbnail(thumbnail);
        details.setTime(time);
        details.setDate(Date);
        list.add(details);
    }

Answer 2

You must first initialize the adapter before calling adapter.notifyDataSetChanged

adapter = new RecyclerViewAdapter(getActivity(), list);
getDatafromFirebase();

Answer 3

To solve this, please move the following lines of code:

adapter = new RecyclerViewAdapter(getActivity(), list);
recyclerView.setAdapter(adapter);

In your onDataChange() method right after:

Log.e("Size",list.get(0).description);

And comment the following line of code because is not needed:

//adapter.notifyDataSetChanged();

In order to make it work, you must initialize and set the adapter inside the callback, otherwise it will always be null due the asynchronous behavior of this method. For this, I recommend you see my answer from this post . You can also take a look at this video for a better understanding.