Firebase android pagination

Question

I\'m building an app which will show videos stored on firebase. The list of videos needs to be paginated fetching most recent 20 videos at a time.

Here is

Answer 1

accepted answear dos not work when less then the max. itmes (21) in database. this is my solution build on the accepted answer:

0)set variables

        private String lastMessageKey;
    private int totalItemCount;
    private int lastVisibleItem;
    private boolean isLoadingMoreFollowers = false;
    private boolean hasMoreItems = true;
    private boolean hasShownNoMoreItemsToast = false;
    private boolean initialLoad = true;
    private final int MAX_LOAD_ITEMS = 11;
    private final int VISIBLE_TRESHOLD = 1;

1) set a listener:

       private void setMessageListener() {

        if (childEventListener == null) {

            mmessageArrayList.clear();
            final ArrayList tempMmessages = new ArrayList<>();
            query = mDatabaseInstace.getReference().child(chat1).child(F.CHATS).child(F.MESSAGES).orderByKey().limitToLast(MAX_LOAD_ITEMS-1);
            childEventListener = new ChildEventListener() {
                @Override
                public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                    Log.d(TAG, "onChildAdded: -----------------> " + dataSnapshot);
                    Log.d(TAG, "onChildAdded: -----------------> " + s);

                    tempMmessages.add(dataSnapshot.getValue(Mmessage.class));
                    preloadMessagePics(tempMmessages);
                    if (initialLoad) {
                        lastMessageKey = tempMmessages.get(0).getMessagePushKey();
                        initialLoad = false;
                    }
                    mmessageArrayList.add(tempMmessages.size()-1, tempMmessages.get(0));
                    messageAdapter.notifyDataSetChanged();
                    tempMmessages.clear();


                }

                @Override
                public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                    Log.d(TAG, "onChildChanged: --------------------------------->");

                }

                @Override
                public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
                    Log.d(TAG, "onChildRemoved: ---------------------------------->");

                }

                @Override
                public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                    Log.d(TAG, "onChildMoved: ------------------------------------>");

                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {
                    Log.d(TAG, "onCancelled: ------------------------------------->");

                }
            };
            query.addChildEventListener(childEventListener);
        }

    }

2) set load more listener:

        private void setLoadMoreListener(){
        setup.RV_messages.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);


                totalItemCount = linearLayoutManager.getItemCount();
                lastVisibleItem = linearLayoutManager.findLastVisibleItemPosition();



                if (!isLoadingMoreFollowers && totalItemCount <= (lastVisibleItem+VISIBLE_TRESHOLD) && (totalItemCount >= MAX_LOAD_ITEMS-1)){

                    if (hasMoreItems) {

                        getMoreMessages();
                        Toast.makeText(homeActivity, "load more items", Toast.LENGTH_SHORT).show();

                    }else {
                        if (!hasShownNoMoreItemsToast) {
                            Toast.makeText(homeActivity, "has no more items", Toast.LENGTH_SHORT).show();
                            hasShownNoMoreItemsToast = true;
                        }
                    }

                }

            }
        });
    }

3) get more items:

       private void getMoreMessages(){

        final ArrayList tempMmessages = new ArrayList<>();

        isLoadingMoreFollowers = true;
        loadMoreQuery = mDatabaseInstace.getReference().child(chat1).child(F.CHATS).child(F.MESSAGES).orderByKey().endAt(lastMessageKey).limitToLast(MAX_LOAD_ITEMS);
        loadMoreChildEventListener = new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

                tempMmessages.add(dataSnapshot.getValue(Mmessage.class));
                preloadMessagePics(tempMmessages);

                if (tempMmessages.size() == MAX_LOAD_ITEMS){

                    lastMessageKey = tempMmessages.get(0).getMessagePushKey();
                    Collections.reverse(tempMmessages);
                    tempMmessages.remove(0);
                    mmessageArrayList.addAll(tempMmessages);
                    isLoadingMoreFollowers = false;
                    messageAdapter.notifyDataSetChanged();
                    tempMmessages.clear();
                    return;
                }


                if (lastMessageKey.equalsIgnoreCase(tempMmessages.get(tempMmessages.size()-1).getMessagePushKey())){

                    Collections.reverse(tempMmessages);
                    tempMmessages.remove(0);
                    mmessageArrayList.addAll(tempMmessages);
                    isLoadingMoreFollowers = false;
                    hasMoreItems = false;
                    messageAdapter.notifyDataSetChanged();
                    tempMmessages.clear();

                }

            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        };
        loadMoreQuery.addChildEventListener(loadMoreChildEventListener);

    }

have fun!!