从 firebase 实时数据库中单个孩子下的多个推送 ID 中检索数据

Question

I am new to android studio and programming and am currently trying to make my first app. In firebase RTDB, I have multiple push ids under a single child that keep on increasing in number as the user presses certain buttons, and they all store only an integer. I want to retrieve the data from all those push ids(or keys, I don't really know what they are actually called) under the child and then sum the integers up and display the result in a textView and do it every time a new field is added. How can I do that? So far I only know how to normally send and receive data to childs sub-childs like this but i have never ever used push ids or keys before:

String recieve = datasnapshot.child("Child").child("subchild").getText().toString();

String send = "send";

databaseReferenc.child("Child").child("sunchile").setValue(send);

The data tree in firebase is as follows:

Answer 1

Assuming that Australia is a direct child of your Firebase Realtime Database root, to sum all those values, please use the following lines of code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference australiaRef = rootRef.child("Australia");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        int total = 0;
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String value = Integer.parseInt(ds.getValue(String.class));
            total += value;
        }
        Log.d("TAG", "total: " + total);
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d("TAG", databaseError.getMessage()); //Don't ignore potential errors!
    }
};
australiaRef.addListenerForSingleValueEvent(valueEventListener);

One more thing. Because you are storing numbers, it best to store them as long values and not as String values.