我不知道如何从Firebase实现无限滚动代码

Question

这是我在我的应用中显示NewsFeed的活动。 我可以从Firebase实时数据库中读取NewsFeed的数据。

public class LoggedActivity extends AppCompatActivity {

private Button logOutButton, postPageButton;
private Session session;
private RecyclerView mPostList;
private DatabaseReference mDatabase;
private DocumentReference postRef;
private static Activity thisActivity = null;
private LinearLayoutManager mLayoutManager;
private boolean userScrolled = false;
private int pastVisiblesItems, visibleItemCount, totalItemCount;
private int itemsPerPage = 2;
private int currentPage = 0;
public static int orderNum = 1;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_logged);

    thisActivity = this;

    mDatabase = FirebaseDatabase.getInstance().getReference().child("post");

    mPostList = findViewById(R.id.post_list);
    mPostList.setHasFixedSize(true);
    mLayoutManager = new LinearLayoutManager(this);
    mPostList.setLayoutManager(mLayoutManager);

}
@Override
protected void onStart() {
    super.onStart();

    final Query DBquery = FirebaseDatabase.getInstance().getReference().child("post").orderByChild("count");

    final FirebaseRecyclerAdapter<Post, PostViewHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Post, PostViewHolder>(
            Post.class,
            R.layout.post_row,
            PostViewHolder.class,
            DBquery
//                mDatabase
    ) {
        @Override
        protected void populateViewHolder(PostViewHolder viewHolder, Post model, int position) {

            viewHolder.setTitle(model.getTitle());
            viewHolder.setDesc(model.getDesc());
            viewHolder.setImage(getApplicationContext(), model.getImage());
            viewHolder.setDate(model.getDate());
            viewHolder.init(position, model);
        }
    };
    mPostList.setAdapter(firebaseRecyclerAdapter);

这是新闻Feed中的ScrollListener。 它工作正常。

    mPostList.addOnScrollListener(new RecyclerView.OnScrollListener() {

        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);

            if (newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL){
                userScrolled = true;
            }
        }
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);

            visibleItemCount = mLayoutManager.getChildCount();
            totalItemCount = mLayoutManager.getItemCount();
            pastVisiblesItems = mLayoutManager
                    .findFirstVisibleItemPosition();

但问题出在这里。 在这个if语句中，我需要从实时数据库中获取新数据。 但我不知道该怎么做。

            if (userScrolled && (visibleItemCount + pastVisiblesItems) == totalItemCount){
                userScrolled = false;
                // fetch new data here.
            }

        }
    });
}

public static class PostViewHolder extends RecyclerView.ViewHolder {

    View mView;

    public PostViewHolder(View itemView) {
        super(itemView);

        mView = itemView;
    }

    public void setTitle(String title){
        TextView post_title = mView.findViewById(R.id.post_title);
        post_title.setText(title);
    }

    public void setDesc(String desc){

        TextView post_desc = mView.findViewById(R.id.post_desc);
        post_desc.setText(desc);
    }

    public void setImage(Context ctx, String image){
        ImageView post_image = mView.findViewById(R.id.post_image);
        Glide.with(ctx)
                .load(image)
                .into(post_image);
    }

    public void setDate(String date){

        TextView post_date = mView.findViewById(R.id.post_date);
        post_date.setText(date);
    }
  }
}
}

此代码为Post.java Class

public class Post {


private String title, desc, image, date;

public Post(){

}

public Post(String title, String desc, String image, String date) {
    this.title = title;
    this.desc = desc;
    this.image = image;
    this.date = date;
}

public String getTitle() {
    return title;
}

public String getDesc() {
    return desc;
}

public String getDate() {
    return date;
}

public void setTitle(String title) {
    this.title = title;
}

public void setDesc(String desc) {
    this.desc = desc;
}

public String getImage() {
    return image;
}

public void setImage(String image) {
    this.image = image;
}

public void setDate(String date){
    this.date = date;
}

}