Calculating child node values in firebase

Question

I'm trying to add the quantity from each userid and display the total figure in a textview.

I have a sample code but it is not working

final  TextView Quant = (TextView)findViewById(R.id.Quant);
    DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference().child("History");
    mDatabase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            int sum = 0;
            for(DataSnapshot ds : dataSnapshot.getChildren())
            {
                Map<String,Object> map = (Map<String,Object>)ds.getValue();
                Object Quantity = map.get("Quantity");
                int pValue = Integer.parseInt(String.valueOf(Quantity));
                sum += pValue;
                Quant.setText(String.valueOf(sum));
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

Answer 1

Change this:

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference().child("History");

to this:

DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference().child("history");

history is lowercase in your database, should be the same here also