Android和Firebase检索有关电子邮件的数据

Question

我正在Firebase和Android上工作，我想从Firebase数据库中检索有关收据电子邮件的数据，有人可以将我从这种情况中拖出来吗？一些代码或StackOverflow帖子或视频参考也将非常有用，因为它们易于区分。enter image description here

 private ListView mlistView;
private ArrayList<String> list;
private ArrayAdapter<String> adapter;
private DatabaseReference ref;
private FirebaseDatabase database;
private RecieptClass fooditem;
private FirebaseAuth auth;
private FirebaseUser user;
private String email;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_reciept);

    final FirebaseUser user = auth.getInstance().getCurrentUser();
    email = user.getEmail();
    fooditem = new RecieptClass();
    mlistView = (ListView)findViewById(R.id.EstlistView);
    database = FirebaseDatabase.getInstance();
    ref = database.getReference("RecieptData");

    list = new ArrayList<>();
    adapter = new ArrayAdapter<String>(this,R.layout.reciept_list_item,R.id.ItemRecieptList,list);

    ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for(DataSnapshot ds : dataSnapshot.getChildren()) {
                if (email == fooditem.getEmail()) {
                    fooditem = ds.getValue(RecieptClass.class);
                    list.add(fooditem.getQuantity() + " " + fooditem.getItemName() + " " + fooditem.getTotalPrice());
                    mlistView.setAdapter(adapter);
                }
            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });
}