如何使用快照侦听器在recyclerview中获取实时更新？

Question

下面是我用来在recyclerview中检索文档数据的代码。工作正常。但是，无论何时添加新文档，它都不会实时更新。我知道快照侦听器仅用于此目的，但很难使其工作。任何帮助将不胜感激。:)

 mFirestore.collection("Users").get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()){
                    for (DocumentSnapshot document : task.getResult()) {
                        Message message = document.toObject(Message.class);
                        messageList.add(message);
                        mAdapter.notifyDataSetChanged();
                    }
                }
            }
        });

Answer 1

您应该像这样将快照事件分开..然后您可以轻松地找出问题所在

mFirestore.collection("Users")
        .addSnapshotListener(new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(@Nullable QuerySnapshot snapshots,
                                @Nullable FirebaseFirestoreException e) {
                if (e != null) {
                    Log.w("TAG", "listen:error", e);
                    return;
                }

                for (DocumentChange dc : snapshots.getDocumentChanges()) {
                    switch (dc.getType()) {
                        case ADDED:
                            Log.d("TAG", "New Msg: " + dc.getDocument().toObject(Message.class));
                            break;
                        case MODIFIED:
                            Log.d("TAG", "Modified Msg: " + dc.getDocument().toObject(Message.class));
                            break;
                        case REMOVED:
                            Log.d("TAG", "Removed Msg: " + dc.getDocument().toObject(Message.class));
                            break;
                    }
                }

            }
        });

可能是由[MODIFIED]事件而非[ADDED]事件触发的快照。