从云FireStore Android读取数据

此脚本是否错误,因为我收到的数据是 null 我在云Firestore上添加了数据。我不使用 RecyclerView 因为我只需要一个数据。

以下是脚本:

private void getCustomer(){
        firestoreDB.collection("customer")
                .get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()) {
                            customers = new ArrayList<>();
                            for (DocumentSnapshot doc : task.getResult()) {
                                Customer customer = doc.toObject(Customer.class);
                                customer.setId_customer(doc.getId());
                                customers.add(customer);
                            }
                        } else {
//                            Log.d(TAG, "Error getting documents: ", task.getException());
                        }
                    }
                });

        firestoreListener = firestoreDB.collection("customer")
                .addSnapshotListener(new EventListener<QuerySnapshot>() {
                    @Override
                    public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
                        if (e != null) {
//                            Log.e(TAG, "Listen failed!", e);
                            return;
                        }
                        customers = new ArrayList<>();
                        for (DocumentSnapshot doc : documentSnapshots) {
                            Customer customer = doc.toObject(Customer.class);
                            customer.setId_customer(doc.getId());
                            customers.add(customer);
                        }
                    }
                });

        id_customer = customers.get(0).getId_customer();
    }

这是我的firestore: