如何从循环中获取Firestore数据并将其发送到recyclerview适配器 [英] How to get firestore data from a loop and send to recyclerview adaptor

问题描述

我正在将数据从Firestore加载到Recycler View Android中.这是一种用于存储商品的Uid的电子商务购物车系统.

I am loading data from firestore into recycler view android. It is a kind of e-commerce cart system in which the items' Uids are stored.

我有我的uid的ArrayList(我已经从firestore收到它了)，现在，我需要通过循环uids Arraylist并将其添加到 documentSnapshots Arraylist.
我尝试了以下方法:

I have my ArrayList of uids(I've already received it from firestore) and now with it, I need to get DocumentSnapshots of the items by looping the uids Arraylist and adding it to a documentSnapshots Arraylist.
I have tried the following:

ArrayList<DocumentSnapshot> documentSnapshots = new ArrayList<>();
                    
      //getting the document snapshot out of the uids
      for (int i = 0 ; i < uids.size() ; i++){
                        
                 db.collection("items").document(uids.get(i)).get()
                   .addOnCompleteListener(task1 -> {

                                    documentSnapshots.add(task1.getResult());
                                    
                                });
                    }  

然后，在获取这些数据之后，将这个数组列表发送给适配器，如下所示:

Then, after getting this data, I send this arraylist to the adaptor as follows:

//sending data to adaptor
adaptorCart = new AdaptorCart(Cart.this , modelCart , db , documentSnapshots);

但是由于onCompletelistener的异步行为，我总是将DocumentSnapshots Arraylist设为空，因此在这种行为下如何像往常一样实现自己想要的功能，我会得到一个空列表.另外，我尝试使用回调，但无法解决问题.

But I always get the DocumentSnapshots Arraylist empty as because of the asynchronous behaviour of the onCompletelistener so how can I achieve what I want as always in this type of behaviour, I would get an empty list. Also, I tried using callback but couldn't get around the problem.

任何帮助将不胜感激！

推荐答案

您可以这样做

     ArrayList<DocumentSnapshot> documentSnapshots = new ArrayList<>();
                
  //getting the document snapshot out of the uids
  int count = uids.size();
  for (int i = 0 ; i < uids.size() ; i++){
                    
             db.collection("items").document(uids.get(i)).get()
               .addOnCompleteListener(task1 -> {

                                documentSnapshots.add(task1.getResult());
                                if(documentSnapshots.size() == count){
                                  adaptorCart = new AdaptorCart(Cart.this , modelCart , db , documentSnapshots);
                                }
                                
                            });
                }  

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