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

You want to be using the limitToFirst/limitToLast methods to retrieve a limited number of results.

videosQuery.orderByKey().limitToFirst(20)

https://www.firebase.com/docs/web/api/query/limittofirst.html

You should really consider changing the naming convention of your videos to include leading 0s (i.e. video01, video02... video10, video11) because the above code will display them exactly as you have them above (which I assume is out of order?)

Alternatively, if you're adding the videos via Java, you could just let firebase create the uniqueids via push(). The uniqueid are generated in a way that they'll sort chronilogically, which sounds like it'll suit your need to grab the most recent(ly added?) videos.

https://www.firebase.com/docs/web/api/firebase/push.html

Answer 2

Android paging library can be used to implement pagination for data fetched from firebase database. Data is displayed in recycler view and paging component fetches pages in response to user scroll events.

Paging data source calls your firebase DAO object passing query parameters for the page to be displayed and results are passed back to paging component using callback provided to it.

Here is a complete example for reference http://www.zoftino.com/firebase-pagination-using-android-paging-library

Answer 3

 mPageEndOffset = 0;
 mPageLimit = 10;


 mPageEndOffset += mPageLimit;

 deviceListQuery = mDatabase.child("users")
 .orderByChild("id").limitToFirst(mPageLimit).startAt(mPageEndOffset);

 deviceListQuery.addValueEventListener(YourActivity.this);

Answer 4

This is how I implemented pagination from firebase database. Consider a case if we have 100 messages. So I first load last 20 messages from firebase i.e. 81 to 100. Then on scroll up I call getMoreMessages() function to load next 20 messages which are 61 to 80 and so on.

public class ChatActivity extends Activity {

        String chat_id = "";
        long mTotalChildren = 0;
        boolean loading = false;
        ChildEventListener childEventListenerMain, childEventListenerPager;
        ChatActivity mContext = ChatActivity.this;
        MessageAdapter messageAdapter;
        @BindView(R.id.pb_messages)
        ProgressBar pb_messages;
        @BindView(R.id.ll_audio)
        LinearLayout llAudio;
        @BindView(R.id.tv_record_time)
        AppCompatTextView tvRecordTime;
        @BindView(R.id.tv_cancel)
        AppCompatTextView tvCancel;
        @BindView(R.id.iv_send)
        AppCompatImageView ivSend;
        @BindView(R.id.iv_record)
        AppCompatImageView ivRecord;
        @BindView(R.id.ab_layout)
        AppBarLayout abLayout;
        @BindView(R.id.messages)
        RecyclerView rvMessages;
        @BindView(R.id.iv_chat_icon)
        SimpleDraweeView ivChatIcon;
        @BindView(R.id.iv_camera)
        AppCompatImageView ivCamera;
        @BindView(R.id.iv_gallery)
        AppCompatImageView ivGallery;
        @BindView(R.id.message_input)
        AppCompatEditText messageInput;
        @BindView(R.id.tv_send)
        AppCompatTextView tvSend;
        @BindView(R.id.toolbar_title)
        AppCompatTextView toolbarTitle;
        @BindView(R.id.toolbar_status)
        AppCompatTextView toolbarStatus;
        @BindView(R.id.ll_send)
        LinearLayout llSend;
        int categoryId, senderId, receiverId, offerId;
        String mLastKey;
        LinearLayoutManager layoutManager;
        private ArrayList<MessageModel> messageArrayList = new ArrayList<>();
        private ArrayList<MessageModel> tempMessageArrayList = new ArrayList<>();

        @Override
        public int getLayoutId() {
            return R.layout.activity_chat;
        }

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

            messageAdapter = new MessageAdapter(mContext, messageArrayList) {

            };

            layoutManager = new LinearLayoutManager(mContext);

            rvMessages.setLayoutManager(layoutManager);
            rvMessages.setItemAnimator(new DefaultItemAnimator());
            rvMessages.setAdapter(messageAdapter);
            rvMessages.setHasFixedSize(true);

            rvMessages.addOnScrollListener(new RecyclerView.OnScrollListener() {
                @Override
                public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                    super.onScrollStateChanged(recyclerView, newState);
                }

                @Override
                public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                    super.onScrolled(recyclerView, dx, dy);

                    if (messageArrayList.size() >= 20 &&
                            !loading && layoutManager.findFirstVisibleItemPosition() == 0 && messageArrayList.size() < mTotalChildren) {

                        loading = true;
                        getMoreMessages();
                    }
                }
            });

            messageAdapter.notifyDataSetChanged();

            //used to scroll up recyclerview when keyboard pops up
            rvMessages.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
                @Override
                public void onLayoutChange(View view, int left, int top, int right, int bottom,
                                           int oldLeft, int oldTop, int oldRight, int oldBottom) {
                    if (bottom < oldBottom) {
                        rvMessages.postDelayed(new Runnable() {
                            @Override
                            public void run() {
                                rvMessages.scrollToPosition(messageArrayList.size() - 1);
                            }
                        }, 100);
                    }
                }
            });

            loading = true;
            getMessages();
        }

        public void getMessages() {

            FirebaseDatabase.getInstance().getReference().child(pathtomsgs).addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    Log.e("childrenCount", String.valueOf(+dataSnapshot.getChildrenCount()));
                    mTotalChildren = dataSnapshot.getChildrenCount();
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });


            Query messageQuery = FirebaseDatabase.getInstance().getReference().child(pathtomsgs).limitToLast(20);

            childEventListenerMain = new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {

                    loading = true;
                    MessageModel messageModel = dataSnapshot.getValue(MessageModel.class);
                    if (messageModel != null) {
                        messageModel.chat_id = chat_id;
                        messageModel.message_id = dataSnapshot.getKey();
                        messageArrayList.add(messageModel);
                        messageAdapter.notifyDataSetChanged();
                        mLastKey = messageArrayList.get(0).message_id;
                        rvMessages.scrollToPosition(messageArrayList.size() - 1);
                    }
                }

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

                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

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

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    Toast.makeText(mContext, "Problem loading more images...", Toast.LENGTH_LONG).show();
                }
            };

            messageQuery.addChildEventListener(childEventListenerMain);

            ValueEventListener messageChildSINGLEValueEventListener = new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    pb_messages.setVisibility(View.GONE);
                    System.out.println("We're done loading messages " + dataSnapshot.getChildrenCount() + " items");
                    loading = false;
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            };

            messageQuery.addListenerForSingleValueEvent(messageChildSINGLEValueEventListener);
        }

        public void getMoreMessages() {
            tempMessageArrayList.clear();

            Query messageQuery = FirebaseDatabase.getInstance().getReference().child(pathtomsgs).orderByKey().endAt(mLastKey).limitToLast(20);

            childEventListenerPager = new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                    loading = true;
                    MessageModel messageModel = dataSnapshot.getValue(MessageModel.class);
                    if (messageModel != null) {

                        messageModel.chat_id = chat_id;
                        messageModel.message_id = dataSnapshot.getKey();
                        tempMessageArrayList.add(messageModel);
                    }
                }

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

                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

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

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    Toast.makeText(mContext, "Problem loading more images...", Toast.LENGTH_LONG).show();
                }
            };

            messageQuery.addChildEventListener(childEventListenerPager);

            ValueEventListener messageChildSINGLEValueEventListener = new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    System.out.println("We're done loading messages " + dataSnapshot.getChildrenCount() + " items");

                    tempMessageArrayList.remove(tempMessageArrayList.size() - 1);

                    messageArrayList.addAll(0, tempMessageArrayList);
                    mLastKey = messageArrayList.get(0).message_id;
                    messageAdapter.notifyDataSetChanged();
                    //rvMessages.scrollToPosition(20);
                    layoutManager.scrollToPositionWithOffset(19, 0);
                    loading = false;
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            };

            messageQuery.addListenerForSingleValueEvent(messageChildSINGLEValueEventListener);
        }


        @Override
        protected void onDestroy() {

            FirebaseDatabase.getInstance().getReference().child(pathtomsgs).removeEventListener(childEventListenerPager);
            FirebaseDatabase.getInstance().getReference().child(pathtomsgs).removeEventListener(childEventListenerMain);

            super.onDestroy();
        }
    }