我如何不重复地从firebase数据库中获取数据

Question

I am developing a android app work with the firebase database, when the user add item to the database the app display it at the Realtime and that what I want, but the problem it is that same item show more than one time in the RecyclerView this is the code that I try

 data = new ArrayList<>();

DatabaseReference myRef = FirebaseDatabase.getInstance().getReference().child("workers");
    myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            if (snapshot.exists()) {
                e_iv.setVisibility(View.GONE);
                e_tv.setVisibility(View.GONE);
                rv_all.setVisibility(View.VISIBLE);
                for (DataSnapshot ds : snapshot.getChildren()) {
                    for (DataSnapshot d : ds.getChildren()) {
                        data.add(d.getValue(work.class));
                    }
                    
                }
                mAdapter = new aAdapter(data);

                rv_all.setAdapter(allGamesAdapter);
                mAdapter.notifyDataSetChanged();
            }

But it does not solve it,and a side note when I go out from the app and enter again it is works perfectly and show the items without repeat anyone,How can I solve that?

Answer 1

What happening is the ArrayList is getting data added every time listener returns the data. To remove duplicacy just clear the arrayllist inside the onDataChange() function

data = new ArrayList<>();

DatabaseReference myRef = 
FirebaseDatabase.getInstance().getReference().child("workers");
myRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        if (snapshot.exists()) {

            data.clear();

            e_iv.setVisibility(View.GONE);
            e_tv.setVisibility(View.GONE);
            rv_all.setVisibility(View.VISIBLE);
            for (DataSnapshot ds : snapshot.getChildren()) {
                for (DataSnapshot d : ds.getChildren()) {
                    data.add(d.getValue(work.class));
                }
                
            }
            mAdapter = new aAdapter(data);

            rv_all.setAdapter(allGamesAdapter);
            mAdapter.notifyDataSetChanged();
        }

Hope your bug is resolved.