Cannot get list size from Firebase on Android

Question

My log can print all Exercise object. But listExercise is null when I call. What's the problem?

ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot snapshot) {
            for (DataSnapshot postSnapshot : snapshot.getChildren()) {
                Exercise exercise = postSnapshot.getValue(Exercise.class);
                String temp = exercise.toString();
                Log.d("exercise: ", temp + "\n"); // can log all
                listExercises.add(exercise);
            }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {
            Log.d("The read failed: ", firebaseError.getMessage());
        }
    });
Log.d("LISTSIZE: ", String.valueOf(listExercises.size())); // return 0

[UPDATE] The answer for anyone need:

@Override
        public void onDataChange(DataSnapshot snapshot) {
            for (DataSnapshot postSnapshot : snapshot.getChildren()) {
                Exercise exercise = postSnapshot.getValue(Exercise.class);
                listExercises.add(exercise);
            }
            // action with data here
            Exercise ex = listExercises.get(0);
            tvQuestion.setText(ex.getQuestion);
        }

No, It just return an empty list when I logged: Log.d("LISTSIZE: ", String.valueOf(listExercises.size())); — kidsoul
– kidsoul, Commented Apr 18, 2016 at 8:53
Probably you are checking the list before Exercise has been inserted. Notice this works asynchronously. Put the Log of "LISTSIZE" after listExercises.add(exercise); — jDur
– jDur, Commented Apr 18, 2016 at 9:02
Of course, I put Log of "LISTSIZE" after listExercises.add(exercise); I will edit my question for more detail. — kidsoul
– kidsoul, Commented Apr 18, 2016 at 9:06
Is your listExcercise a custom implementation of List or is class Exercise doing something in the method toString(); Maybe if you put the rest of the code I can help you better :) — jDur
– jDur, Commented Apr 18, 2016 at 9:09

jDur · Accepted Answer · 2016-04-18 09:44:14Z

3

When the method "paintListInScreen" is called, you know for sure the list have some content (or maybe not, that depends on the server, but you are being consistent with threads).

ref.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot snapshot) {
        for (DataSnapshot postSnapshot : snapshot.getChildren()) {
            Exercise exercise = postSnapshot.getValue(Exercise.class);
            String temp = exercise.toString();
            Log.d("exercise: ", temp + "\n"); // can log all
            listExercises.add(exercise);
        }
         Log.d("LISTSIZE: ", String.valueOf(listExercises.size())); // return 0
        paintListInScreen(listExercises);
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {
        Log.d("The read failed: ", firebaseError.getMessage());
    }
});

answered Apr 18, 2016 at 9:44

jDur

1,4919 silver badges10 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

kidsoul Over a year ago

Thanks I will try it

kidsoul Over a year ago

You are correct, jDur. After I tried, I found it two point for we can use data I get: The first, it's time after onDataChange method. The second, when you do some action after sync data, maybe it's onClick of button...etc..

jDur Over a year ago

Your welcome :). If you think this is a correct answer please mark it as correct so other users could find it helpful.

Saurabh Padwekar · Accepted Answer · 2016-11-12 12:08:08Z

0

For Java 8 and newer versons (For Android API Level 24 is required ):

int size = dataSnapshot.getChildren().spliterator().getExactSizeIfKnown() ;

For Older Versions:

int size = 0 
for (DataSnapshot postSnapshot : snapshot.getChildren()) {
    size++ ;
}

edited Nov 12, 2016 at 12:08

answered Nov 12, 2016 at 12:02

Saurabh Padwekar

4,0841 gold badge37 silver badges37 bronze badges

1 Comment

Zain Over a year ago

the top one also requires API 24

Zain · Accepted Answer · 2019-09-14 04:32:10Z

0

To get the size of datasnapshot object:

dataSnapshot.getChildrenCount();

answered Sep 14, 2019 at 4:32

Zain

41.3k10 gold badges71 silver badges95 bronze badges

Collectives™ on Stack Overflow

Cannot get list size from Firebase on Android

3 Answers 3

3 Comments

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related