addSnapshotListener再次获取所有数据，而不是仅有的更改

Question

我正在尝试制作聊天应用程序，但我有一个问题，获取实时更改，我尝试使用文档并成功地进行了分页，但当我调用addSnapshotListener时，我再次获得了所有文档，不仅是更改，而且当我尝试检查我获得的数据是否被收获时，应用程序崩溃了！我也试图使它在列表的开始，所以任何一个可以帮助我什么是错误的代码！！

从FireStore获取所有列表：

 private void getList() {
    String myId = mAuth.getUid();
    String id = getIntent().getStringExtra("id");
    messageItems = new ArrayList<>();

    Query first = db.collection("ChatUsers")
            .document(myId)
            .collection(id)
            .orderBy("time", Query.Direction.DESCENDING)
            .limit(10);
    first.get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
        @Override
        public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
            for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots){
                String name = documentSnapshot.get("name").toString();
                String message = documentSnapshot.get("message").toString();
                String messageId = documentSnapshot.getId();
                String userId = documentSnapshot.get("userId").toString();
                Long timee = (Long) documentSnapshot.get("time");
                MessageItem messageItem = new MessageItem(message,messageId,name,userId,timee);

                messageItems.add(messageItem);
                adapter.notifyDataSetChanged();
            }

            if (queryDocumentSnapshots.size() >= 10) {
                lastVisible = queryDocumentSnapshots.getDocuments()
                        .get(queryDocumentSnapshots.size() -1);
                Query next = db.collection("ChatUsers")
                        .document(myId)
                        .collection(id)
                        .orderBy("time", Query.Direction.DESCENDING)
                        .startAfter(lastVisible)
                        .limit(10);
                next.get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                    @Override
                    public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                        for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots){
                            String name = documentSnapshot.get("name").toString();
                            String message = documentSnapshot.get("message").toString();
                            String messageId = documentSnapshot.getId();
                            String userId = documentSnapshot.get("userId").toString();
                            Long timee = (Long) documentSnapshot.get("time");
                            MessageItem messageItem = new MessageItem(message,messageId,name,userId,timee);

                            messageItems.add(messageItem);
                        }
                        addOnChangeListener(messageItems,id,myId);
                        lastVisible = queryDocumentSnapshots.getDocuments()
                                .get(queryDocumentSnapshots.size() -1);

                    }
                });
            }

        }
    });

}

以下是我从ChangeListener获得的信息：

private void addOnChangeListener(List<MessageItem> messageItems, String id, String myId) {
    if (messageItems.size()>0){
        db.collection("ChatUsers")
                .document(myId)
                .collection(id)
                .orderBy("time", Query.Direction.ASCENDING)
                .addSnapshotListener(new EventListener<QuerySnapshot>() {
                    @Override
                    public void onEvent(@Nullable QuerySnapshot value, @Nullable FirebaseFirestoreException error) {
                        for (DocumentChange dc : value.getDocumentChanges()){
                            String name = dc.getDocument().get("name").toString();
                            String message = dc.getDocument().get("message").toString();
                            String messageId =dc.getDocument().getId();
                            String userId = dc.getDocument().get("userId").toString();
                            Long time = (Long) dc.getDocument().get("time");
                            MessageItem messageItem = new MessageItem(message,messageId,name,userId,time);
                            Log.i("messageId",messageId);
                            messageItems.add(0,messageItem);
                            adapter.notifyDataSetChanged();
                        }

                    }
                });
    }

}

Answer 1

您所描述的是预期的行为：当附加快照侦听器时，它读取集合中存在的或与查询匹配的所有数据。

如果您想要获得该数据的子集，您应该在查询中添加条件以仅检索该子集。例如，仅获取已修改数据的一种常用方法是在每个设置为FieldValue.ServerTimestamp()的文档中存储LastModified字段，然后仅查询LastModified晚于“now”的文档。