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

I recommend you see the last part of my anwser from this **[post](https://stackoverflow.com/questions/47847694/how-to-return-datasnapshot-value-as-a-result-of-a-method/47853774)** and also take a look at this **[video](https://www.youtube.com/watch?v=OvDZVV5CbQg)** to better understand why you have this behaviour. — Alex Mamo, Jul 20 '18 at 17:47

prashant17 · Accepted Answer · 2018-07-20T10:58:01.423

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) {

        }
    });

i have tried this before, but when i tried to display tempRecord data it become null again when outside onDataChanged() — CJ Yeo, Jul 20 '18 at 10:46
its because your `display tempRecord` code is executed before `onDataChange` is called as Firebase fetches data `asynchronously` — prashant17, Jul 20 '18 at 10:55
Still having problem when i try to display data. 07-20 18:59:43.072 15830-15830/com.example.cheejin.fyp E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.cheejin.fyp, PID: 15830 java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Double com.example.cheejin.fyp.UserFoodRecord.getGoal()' on a null object reference at com.example.cheejin.fyp.AddFragment$2.onClick(AddFragment.java:164) — CJ Yeo, Jul 20 '18 at 11:01
post line of code where you are getting NullPointerException. `UserFoodRecord.getGoal() must be NULL` — prashant17, Jul 20 '18 at 11:08
Now i able to get the data as long as i do all my method inside onDataChanged() method. Thanks for helping. — CJ Yeo, Jul 21 '18 at 07:56

Retrieve data from firebase return null in onCreateView

1 Answers1