如何遍历购物车中的物品，2)将每个物品添加到新位置，3)从旧位置删除物品 [英] How can I loop over the items in the cart, 2) Add each item to the new location, 3) Delete the item from the old location

问题描述

正在使用Recycler firestore Adapter显示项目.我希望将recyclerview视图中的项目添加到另一个数据库中，并通过单击按钮清除初始数据库.我尝试了此操作，但出现了一个错误，即com.google.firebase.firestore.QuerySnapshot无法转换为java.util.List

The items are being displayed using Recycler firestore Adapter. I want to have the items in the recyclerview view to be added in another database and the initial database cleared by a click of a button. I tried this but I got the error that com.google.firebase.firestore.QuerySnapshot cannot be cast to java.util.List

public void placeOrder() {

    FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
    Query query = rootRef
            .collection(String.valueOf(new 
  StringBuffer("/").append(user.getUid()).append("cart")));

    Task task = query.get();

    task.addOnSuccessListener(new OnSuccessListener<List<Object>>() {

        @Override
        public void onSuccess(List<Object> list) {


            CollectionReference notebookRef;
            mAuth = FirebaseAuth.getInstance();
            user = mAuth.getCurrentUser();
            if (user != null) {
                notebookRef = db.collection(String.valueOf(new 
        StringBuffer("/").append(user.getUid()).append("order")));



                String name = String.valueOf(list.get(1));
                String delivery = String.valueOf(list.get(2));
                String amount = String.valueOf(list.get(3));

                OrderItem orderItem = new OrderItem(name, amount, 
                delivery);
                notebookRef.add(orderItem);
                Toast.makeText(context, "Items Added", 
                     Toast.LENGTH_SHORT).show();
            }
           }
        });
       }[![This is my Database][1]][1]

推荐答案

The Query.get() method returns a Task<QuerySnapshot>. Since you declared a Task<List> in your code, this results in the error that you get: com.google.firebase.firestore.QuerySnapshot cannot be cast to java.util.List.

请阅读从集合中读取多个文档的文档，因为它包含您需要的精确代码段.

Please study the documentation on reading multiple documents from a collection, as it contains the precise code snippet you need.

尽管您要从一个集合中获取整个集合还是单个文档，但我还是不能完全确定.您可以这样初始化query:

One thing I'm not completely sure of though it whether you are getting an entire collection or a single document from a collection. You initialize query like this:

Query query = rootRef.collection(
  String.valueOf(new StringBuffer("/").append(user.getUid()).append("cart")));

据我所知，这导致了"/uidOfUser/cart"的路径，该路径将指向以当前用户命名的集合中的cart 文档.如果确实是您的数据库结构，则需要遵循获取单个文档，该文档将返回Task<DocumentSnapshot>.

As far as I can see this leads to a path of "/uidOfUser/cart", which would point to the cart document in a collection named after the current user. If that is indeed your database structure, you'll need to follow the example from the documentation on getting a single document, which returns a Task<DocumentSnapshot>.

这篇关于如何遍历购物车中的物品，2)将每个物品添加到新位置，3)从旧位置删除物品的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！