Firebase在模拟器和Android设备上获取2个不同的输出结果

Question

以下是Firebase中存储的内容：

  "73668" : {
    "id" : "73668",
    "price" : "Price",
    "product1" : "1. Product 1",
    "product2" : "2. Product 2",
    "product3" : "3. Product 3",
    "status" : "not ready"
  },
  "a2521" : {
    "id" : "a2521",
    "price" : "Price",
    "product1" : "1. Product 1",
    "product2" : "2. Product 2",
    "product3" : "3. Product 3",
    "status" : "not ready"
  },
  "a719b" : {
    "id" : "a719b",
    "price" : "Price",
    "product1" : "1. Product 4",
    "product2" : "2. Product 5",
    "product3" : "3. Product 6",
    "status" : "not ready"
  }
}

以下是在应用程序中获取的方式：

我正在使用的代码：

public ArrayList<Order> getOrders() {

  final Firebase myFirebaseRef = new Firebase("https://torrid-heat-2650.firebaseio.com/orders");
  myFirebaseRef.addListenerForSingleValueEvent(new ValueEventListener() {
    public void onDataChange(DataSnapshot snapshot) {
      for (DataSnapshot child : snapshot.getChildren()) {
        Order order = new Order();
        order.setProduct1(child.child("product1").getValue().toString());
        order.setProduct2(child.child("product2").getValue().toString());
        order.setProduct3(child.child("product3").getValue().toString());
        order.setId(child.child("id").getValue().toString());
        order.setPrice(child.child("price").getValue().toString());

        itemsList.add(order);
      }
    }

    public void onCancelled(FirebaseError firebaseError) {
    }

  });
  System.out.println(itemsList.size());
  return itemsList;
}

相同的操作会在Android设备上返回空的arraylist。有趣的是，它在两种情况下都输出0，但是返回非空的arraylist。什么可能导致相同代码中的2个不同输出？谢谢。