Retrieve data from firebase return null in onCreateView

Question

Success retrieve data in onDataChange method. However, cant retrieve data outside onDataChange method (inside onCreateView). While trying to get data from trackList, it return null.

Below is how i retreive data from firebase and try to display on the view.

currentUser = (User) getArguments().getSerializable("currentUserBundle");

    databaseTracks = FirebaseDatabase.getInstance().getReference("tracks").child(currentUser.getUserId());
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd-MM-yy");
    Date date = new Date();
    todayDate = simpleDateFormat.format(date);

    databaseTracks.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            Iterable<DataSnapshot> children = dataSnapshot.getChildren();

            if (trackList != null) {
                trackList.clear();
            }

            for (DataSnapshot c : children) {
                trackList.add(c.getValue(UserFoodRecord.class));
            }

        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

    if (trackList != null) {
        for (UserFoodRecord u : trackList) {
            //Problem at here !!!!!!
            //return null while try to retrieve data
            dateList.add(u.getDate());
            if (u.getDate() == todayDate) {
                checkTodayRecord = true; //got today record
                UserFoodRecord tempRecord = new UserFoodRecord(u.getDate(), u.getBreakfast(), u.getLunch(), u.getDinner(), u.getOther()
                        , u.getExercise(), u.getGoal(), u.getFood(), u.getExerciseBurn());
                currentUserFoodRecord = tempRecord;
            }
        }
    }

    //return null
    if (currentUserFoodRecord != null) {
        caloriesGoal.setText(currentUserFoodRecord.getGoal().toString());
        caloriesFood.setText(currentUserFoodRecord.getFood().toString());
        caloriesExerc.setText(currentUserFoodRecord.getExerciseBurn().toString());
        caloriesRemain.setText(currentUserFoodRecord.getRemaining().toString());
    }

Data from firebase

Answer 1

Move your code inside onDataChange as Firebase fetches data asynchronously

databaseTracks.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            Iterable<DataSnapshot> children = dataSnapshot.getChildren();

            if (trackList != null) {
                trackList.clear();
            }

            for (DataSnapshot c : children) {
                trackList.add(c.getValue(UserFoodRecord.class));
            }

            if (trackList != null) {
                for (UserFoodRecord u : trackList) {
                    dateList.add(u.getDate());
                    if (u.getDate() == todayDate) {
                        checkTodayRecord = true; //got today record
                        UserFoodRecord tempRecord = new UserFoodRecord(u.getDate(), u.getBreakfast(), u.getLunch(), u.getDinner(), u.getOther()
                                , u.getExercise(), u.getGoal(), u.getFood(), u.getExerciseBurn());
                        currentUserFoodRecord = tempRecord;
                    }
                }
            }


            if (currentUserFoodRecord != null) {
                caloriesGoal.setText(currentUserFoodRecord.getGoal().toString());
                caloriesFood.setText(currentUserFoodRecord.getFood().toString());
                caloriesExerc.setText(currentUserFoodRecord.getExerciseBurn().toString());
                caloriesRemain.setText(currentUserFoodRecord.getRemaining().toString());
            }

        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });