问如何检索Firebase中唯一密钥的所有子节点

EN

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference userLocationRef = rootRef.child("user_Location").child("-KpzaWx6FfdT27FlEoaZ").child("l");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        Double lat = ds.child("0").getValue(Double.class);
        Double long = ds.child("0").getValue(Double.class);
        Log.d("TAG", lat + " / " + long);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
userLocationRef.addListenerForSingleValueEvent(eventListener);