Pagination in endless recycler view with firebase

问题:

I am working on Q/A app . I have successfully loaded questions from firebase . But I am not able to apply pagination from Firebase like database . And how to recognize that we have reached end of recycler view so that next few questions can loaded .

回答1:

To recognize that we have reached end of RecyclerView you can use this class EndlessRecyclerOnScrollListener.java

To load more next question, you should define one more field in Question class like number

public class Question {
    private int number; // it must unique and auto increase when you add new question
    ...
}

Then when you load questions from FireBase you can do like

public class MainActivity extends AppCompatActivity {
    private static final int TOTAL_ITEM_EACH_LOAD = 10;
    private DatabaseReference mDatabase;
    final List<Question> questionList = new ArrayList<>();

    private int currentPage = 0;

    private RecyclerView recyclerView;
    private RecyclerViewAdapter mAdapter; 

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ...
        // init and set layout manager for your RecyclerView
        ...
        mAdapter = new RecyclerViewAdapter(questionList);
        recyclerView.setAdapter(mAdapter);
        recyclerView.setOnScrollListener(new EndlessRecyclerOnScrollListener(mLayoutManager) {
            @Override
            public void onLoadMore(int current_page) { // when we have reached end of RecyclerView this event fired
                loadMoreData();
            }
        });
        loadData(); // load data here for first time launch app
    }

    private void loadData() {
        // example
        // at first load : currentPage = 0 -> we startAt(0 * 10 = 0)
        // at second load (first loadmore) : currentPage = 1 -> we startAt(1 * 10 = 10)
        mDatabase.child("questions")
                .limitToFirst(TOTAL_ITEM_EACH_LOAD)
                .startAt(currentPage*TOTAL_ITEM_EACH_LOAD)
                .orderByChild("number")
                .addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        if(!dataSnapshot.hasChildren()){
                            Toast.makeText(MainActivity.this, "No more questions", Toast.LENGTH_SHORT).show();
                            currentPage--;
                        }
                        for (DataSnapshot data : dataSnapshot.getChildren()) {
                            Question question = data.getValue(Question.class);
                            questionList.add(question);
                            mAdapter.notifyDataSetChanged();
                        }
                    }

                   @Override public void onCancelled(DatabaseError databaseError) {}});
    }

    private void loadMoreData(){
        currentPage++;
        loadData();
    }
}

Here is my DEMO project

回答2:

To check whether you have reached the bottom of the RecyclerView, you can use the onScrolled listener as below, the if condition here is important and it is defining when a user has reached to the bottom.

mRV.addOnScrollListener(new RecyclerView.OnScrollListener() {

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

                mTotalItemCount = mLayoutManager.getItemCount();
                mLastVisibleItemPosition = mLayoutManager.findLastVisibleItemPosition();

                if (!mIsLoading && mTotalItemCount <= (mLastVisibleItemPosition + mPostsPerPage)) {
                    getUsers(mAdapter.getLastItemId());
                    mIsLoading = true;
                }
            }
        });

Secondly, you can use startAt and limitToFirst methods to get questions in batches as shown below:

query = FirebaseDatabase.getInstance().getReference()
                    .child(Consts.FIREBASE_DATABASE_LOCATION_USERS)
                    .orderByKey()
                    .startAt(nodeId)
                    .limitToFirst(mPostsPerPage);

I have created an open source app that shows exactly how it is done. Please have a look: https://blog.shajeelafzal.com/2017/12/13/firebase-realtime-database-pagination-guide-using-recyclerview/

回答3:

You can create Firebase Queries to your FirebaseRecyclerAdapter, using startAt and limitToFirst to download records in batches.

The limitToFirst page size would be increased by and event, such as a click or a pull to refresh.