无法从Android上的Firebase数据库获取数据

Question

So I have a set up where I want to get data from the Database on Firebase, I can get the URL back fine but I can't get data from it. When I try to debug it reads in query.addValueEventListener but after that it just goes straight to my list adapter. I don't know it's not getting the data. I have a similar set up on my node server which works perfectly fine, but won't work on Android for some reason

 final DatabaseReference database = FirebaseDatabase.getInstance().getReference();
Query query = database.child("exercises");
Log.i("Database query", database.child("exercises").toString());
query.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot exerciseSnapshot: dataSnapshot.getChildren())
        {
            List<ExerciseList> exercises = new ArrayList<ExerciseList>();
            ExerciseList exerciseList = exerciseSnapshot.getValue(ExerciseList.class);
            Log.i("description/name", exerciseList.getDescription() + " " + exerciseList.getName());
            exercises.add(exerciseList);
            adapter = new ExerciseLoadListAdapter(mActivity, exercises);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});
mListView.setAdapter(adapter);

Answer 1

its go to adapter directly because addValueEventListener() is Asynchronous listeners , its run in background !

Try this code , it may be help you !

final DatabaseReference database = FirebaseDatabase.getInstance().getReference();
    //Query query = database.child("exercises");
    //Log.i("Database query", database.child("exercises").toString());
    database.child("exercises").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot exerciseSnapshot: dataSnapshot.getChildren())
            {
                List<ExerciseList> exercises = new ArrayList<ExerciseList>();
                ExerciseList exerciseList = exerciseSnapshot.getValue(ExerciseList.class);
                Log.i("description/name", exerciseList.getDescription() + " " + exerciseList.getName());
                exercises.add(exerciseList);

            }
               adapter = new ExerciseLoadListAdapter(mActivity, exercises);
               mListView.setAdapter(adapter)
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

Answer 2

The Firebase do NOT get the data in the debug mode in real time. If you need some object from your firebase database you will need to get the object before. I face this problem a several times, thats why in some cases I use SQLite to store data from Firebase before i take any action. But, in a fragment you can not do that, you need the data in realtime. So you need to store the listener in a variable and use it after. Here in my Github page I have a fragment working fine. ContatsFragment.java []'s