使用firebase在无尽的回收器视图中进行分页

Question

我正在开发 Q/A 应用程序。我已成功加载来自 firebase 的问题。但我无法从像数据库这样的 Firebase 应用分页。以及如何识别我们已经到达回收站视图的末尾，以便可以加载接下来的几个问题。

Answer 1

要识别我们已到达RecyclerView 的末尾，您可以使用此类EndlessRecyclerOnScrollListener.java

要加载更多下一个问题，您应该在Question class 中再定义一个字段，例如数字

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

然后，当您从FireBase 加载问题时，您可以这样做

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

Answer 2

要检查你是否到达了RecyclerView的底部，你可以使用如下的onScrolled监听器，这里的if条件很重要，它定义了用户何时到达底部。

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;
                }
            }
        });

其次，您可以使用startAt和limitToFirst方法批量获取问题，如下所示：

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

我创建了一个开源应用程序，它可以准确地展示它是如何完成的。请看：https://blog.shajeelafzal.com/2017/12/13/firebase-realtime-database-pagination-guide-using-recyclerview/

Answer 3

您可以创建Firebase Queries到您的FirebaseRecyclerAdapter，使用startAt和limitToFirst批量下载记录。

limitToFirst 页面大小会随着事件（例如点击或pull to refresh）而增加。