Reading Data From Firebase realtime database

Question

I'm basically trying to get the values of Key "name" from Firebase then show all the names into a listview. The problem is that my data from Firebase doesn't shows up in the listView even though my code is having no errors.

Firebase Structure: MY FIREBASE DATABASE STRUCTURE

My Code:

List<String> list = new ArrayList<>();

    list.addAll(FFunc());

    Toast.makeText(this, "Success!", Toast.LENGTH_SHORT).show();

    ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, R.layout.activity_listview, R.id.textView, list);
    simpleListView.setAdapter(arrayAdapter);

    public List<String> FFunc(){

    final List<String> arr = new ArrayList<>();

    DatabaseReference database = FirebaseDatabase.getInstance().getReference("Employee");
    DatabaseReference myRef = database.child("name");

    myRef.addValueEventListener(new com.google.firebase.database.ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            for(DataSnapshot data : dataSnapshot.getChildren()) {

                String name = data.getValue(String.class).toString();
                arr.add(name);
            }
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {}
    });

    return arr;
}

By using the above code, I'm getting an empty listView with no values from Firebase. Anyone can tell me what's can be the possible solution to this problem. I'm a Beginner in Android thus I have no idea what to do next even after spending 2 whole days on it.

There is no way you can return your `arr` as a result of a method. Please check the duplicate to see why do you have this behavior and how can you solve this using a custom callback. — Alex Mamo, Dec 06 '19 at 17:47

Md. Asaduzzaman · Answer 1 · 2019-12-06T17:57:38.490

Use LiveData as return type and observe the changes of it's value to execute desired operation.

private MutableLiveData<List<String>> userNameMutableLiveData = new MutableLiveData<>();

public MutableLiveData<List<String>> FFunc() {
    final List<String> arr = new ArrayList<>();
    DatabaseReference database = FirebaseDatabase.getInstance().getReference("Employee");
    DatabaseReference myRef = database.child("name");

    myRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            for(DataSnapshot data : dataSnapshot.getChildren()) {

                String name = data.getValue(String.class).toString();
                arr.add(name);
            }

            ....

            userNameMutableLiveData.setValue(arr);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {}
    });

    return userNameMutableLiveData;
}

Then from your Activity/Fragment observe the LiveData and inside onChanged do your desired operation.

List<String> list = new ArrayList<>();
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, R.layout.activity_listview, R.id.textView, list);
simpleListView.setAdapter(arrayAdapter);

....

FFunc().observe(this, new Observer<List<String>>() {
    @Override
    public void onChanged(List<String> names) {
        //here, do whatever you want on `names`

        list = names;
        arrayAdapter.notifyDataSetChanged();
    }
});

@Haseeb, Have you checked that? – Md. Asaduzzaman Dec 09 '19 at 05:39 — Md. Asaduzzaman, Dec 09 '19 at 05:39

Reading Data From Firebase realtime database

1 Answers1