安卓 - 火库无限分页与听众

Question

        我正在制作带有firebase firestore数据库的Android聊天应用程序，我需要与侦听器进行无限分页以进行数据更改（新按摩，删除按摩...

我发现用kotlin和corse搜索的firebase文档写的博客文章，最终得到了这个代码：

    // firstTime variable shows if function is called from pagination or initially

    private void addMessagesEventListener(boolean firstTime) {

            // get collection

            CollectionReference messagesCollection =                         chatsCollection.document(chat.getId()).collection(Constants.FIREBASE_MESSAGES_PATH);

    // create query

    Query query = messagesCollection.orderBy("timestamp", Query.Direction.DESCENDING);

    // if NOT first time add startAt

    if (!firstTime) {

        query.startAt(startTimestamp);

    }

    //limit to 20 messages

    query.limit(20).get().addOnSuccessListener(queryDocumentSnapshots -> {

        if (!firstTime) {

            endTimestamp = startTimestamp;

        }

        startTimestamp = (long) queryDocumentSnapshots.getDocuments().get(queryDocumentSnapshots.size() - 1).get("timestamp");

        Query innerQuery = messagesCollection.orderBy("timestamp").startAt(startTimestamp);

        if(!firstTime) {

            innerQuery.endBefore(endTimestamp);

        }

        ListenerRegistration listener = innerQuery

                .addSnapshotListener((queryDocumentSnapshots1, e) -> {

                    if (e != null) {

                        Log.w(TAG, "listen:error", e);

                        return;

                    }

Answer 1

试试这个&nbsp;@Override&nbsp;public void onStart() {&nbsp; &nbsp; &nbsp; &nbsp; super.onStart();&nbsp; &nbsp; &nbsp; &nbsp; loadFirstQuery();&nbsp;}&nbsp; &nbsp; public void loadFirstQuery() {&nbsp; &nbsp; &nbsp; &nbsp; if (firebaseAuth.getCurrentUser() != null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; contentListDashboard.clear();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; String currentUserId = firebaseAuth.getCurrentUser().getUid();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // what we do when recycler reach bottom&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; recyclerProfileDashboard.addOnScrollListener(new RecyclerView.OnScrollListener() {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;@Override&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;super.onScrolled(recyclerView, dx, dy);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;// horizontal&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;//Boolean reachBottom = !recyclerView.canScrollHorizontally(-1);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;// for vertical recycler&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Boolean reachBottom = !recyclerView.canScrollVertically(-1);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;if (reachBottom) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;loadMorePost(); // do load more post&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;}&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;});&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // RETRIEVING FIRST Query&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Query firstQuery = firebaseFirestore&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .collection("ProfileDashboard")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .document(currentUserId)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .collection("ProfileInfo")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .orderBy("timestamp", Query.Direction.DESCENDING)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .limit(20);&nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; firstQuery.addSnapshotListener(new EventListener<QuerySnapshot>() {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; @Override&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (!documentSnapshots.isEmpty()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // please add if doc not empty&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (isFirstPageFirstLoad) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; lastVisible = documentSnapshots.getDocuments().get(documentSnapshots.size() - 1); // array 0, 1, 2&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (doc.getType() == DocumentChange.Type.ADDED) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //String postId = doc.getDocument().getId();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; contentProfileDashboard = doc.getDocument().toObject(ContentProfileDashboard.class);&nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // if first page firest load true&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (isFirstPageFirstLoad) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; contentListDashboard.add(contentProfileDashboard);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; contentListDashboard.add(0, contentProfileDashboard);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // fire the event&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; adapterProfileDashboard.notifyDataSetChanged();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; isFirstPageFirstLoad = false;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; });&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }&nbsp; &nbsp;// Method to load more post&nbsp; &nbsp;public void loadMorePost() {&nbsp; &nbsp; &nbsp; &nbsp; if (firebaseAuth.getCurrentUser() != null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; String currentUserId = firebaseAuth.getCurrentUser().getUid();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Query nextQuery = firebaseFirestore&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .collection("ProfileDashboard")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .document(currentUserId)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .collection("ProfileInfo")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .orderBy("timestamp", Query.Direction.DESCENDING)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .startAfter(lastVisible)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .limit(20);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; nextQuery.addSnapshotListener(new EventListener<QuerySnapshot>() {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; @Override&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (!documentSnapshots.isEmpty()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; lastVisible = documentSnapshots.getDocuments().get(documentSnapshots.size() - 1);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (doc.getType() == DocumentChange.Type.ADDED) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //String postId = doc.getDocument().getId();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // contentSeen = doc.getDocument().toObject(ContentProfile.class);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // contentList.add(contentSeen);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; contentProfileDashboard = doc.getDocument().toObject(ContentProfileDashboard.class);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; contentListDashboard.add(contentProfileDashboard);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //adapterSeen.notifyDataSetChanged();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; adapterProfileDashboard.notifyDataSetChanged();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; });&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp;}任何问题？

Answer 2

我发现了错误。工作代码是：private void addMessagesEventListener(boolean firstTime) {&nbsp; &nbsp; CollectionReference messagesCollection = chatsCollection.document(chat.getId()).collection(Constants.FIREBASE_MESSAGES_PATH);&nbsp; &nbsp; Query query = messagesCollection.orderBy("timestamp", Query.Direction.DESCENDING);&nbsp; &nbsp; if (!firstTime) {&nbsp; &nbsp; &nbsp; &nbsp; query = query.startAt(startListen);&nbsp; &nbsp; }&nbsp; &nbsp; query.limit(20).get().addOnSuccessListener(queryDocumentSnapshots -> {&nbsp; &nbsp; &nbsp; &nbsp; if (!firstTime) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; endListen = startListen;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; startListen = queryDocumentSnapshots.getDocuments().get(queryDocumentSnapshots.size() - 1);&nbsp; &nbsp; &nbsp; &nbsp; Query innerQuery = messagesCollection.orderBy("timestamp").startAt(startListen);&nbsp; &nbsp; &nbsp; &nbsp; if(!firstTime) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; innerQuery = innerQuery.endBefore(endListen);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; ListenerRegistration listener = innerQuery&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .addSnapshotListener((queryDocumentSnapshots1, e) -> {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (e != null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Log.w("SASA", "listen:error", e);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (DocumentChange dc : queryDocumentSnapshots1.getDocumentChanges()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Message message = dc.getDocument().toObject(Message.class);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; switch (dc.getType()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case ADDED:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // add new message to list&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; messageListAdapter.addMessage(message);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (firstTime) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; messagesList.smoothScrollToPosition(0);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; case REMOVED:&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // remove message from list&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; messageListAdapter.removeMessage(message);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; break;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; });&nbsp; &nbsp; &nbsp; &nbsp; listeners.add(listener);&nbsp; &nbsp; });}错误在于query = query.startAt(startListen)innerQuery = innerQuery.endBefore(endListen)startListen & endListen 是 DocumentSnapshot type我正在使用 sortedList 在我的适配器中你应该添加private void detachListeners() {&nbsp; &nbsp; for(ListenerRegistration registration : listeners) {&nbsp; &nbsp; &nbsp; &nbsp; registration.remove();&nbsp; &nbsp; }}在 onDestroy 中分离所有侦听器。代码正在侦听添加新消息和删除旧消息。