RecyclerView scrolling top when loading new data

问题

I have a problem with RecyclerView. I implemented OnScrollListener to it and when user reach end of list it should load a new data depending on index (index 1 loading first 8 index 2 loading second 8 etc) But problem is as soon as adapter start loading new data it scroll me to top :(

This is my code from function where I'm calling server:

  public void showlist() {
    progressBar = new ProgressDialog(getActivity());
    progressBar.setMessage("Please wait ...");
    progressBar.show();
    NetworkSDK.getInstance().getNews(size, offset, new Callback<List<News>>() {
        @Override
        public void onResponse(Call<List<News>> call, Response<List<News>> response) {
            if (response.code() == 401) {
                Intent intent = new Intent(getContext(), MainPreLogin.class);
                intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NEW_TASK);
                progressBar.dismiss();
                startActivity(intent);
                SharedData.getInstance().removeString("token");


            }
            if (response.isSuccess()) {
                newsAdapter = new NewsAdapterRecycler(listNews);

                if (response.body().size() == 0) {
                    progressBar.dismiss();
                    Toast.makeText(getActivity(), R.string.noMorenews, Toast.LENGTH_SHORT).show();



                } else {
                    for (int i = 0; i < response.body().size(); i++) {
                        newsAdapter.insert(newsAdapter.getItemCount() + 1, response.body().get(i));
                    }
                    newsList.setAdapter(newsAdapter);
                    newsAdapter.notifyDataSetChanged();
                    progressBar.dismiss();



                }

            }
        }

        @Override
        public void onFailure(Call<List<ba.project.models.News>> call, Throwable t) {
            Toast.makeText(getContext(), R.string.errorNoconnection, Toast.LENGTH_LONG).show();
            progressBar.dismiss();


        }
    });

}

This is my adapter:

public class NewsAdapterRecycler extends RecyclerView.Adapter<NewsAdapterRecycler.MyViewHolder> {

private static int selectedItem = -1;
ArrayList<News> newslist;
Context context;

public NewsAdapterRecycler(ArrayList<News> newslist) {

    this.newslist = newslist;

}

@Override
public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    context = parent.getContext();
    View itemView = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.single_news_layout, parent, false);
    return new MyViewHolder(itemView);
}

@Override

public void onBindViewHolder(MyViewHolder holder, int position) {
    View view = null;
    Log.d("Pozicija News",String.valueOf(position));
    News news = newslist.get(position);
    holder.shortText.setText(news.getIntro());
    holder.name.setText(news.getSubject());
    if (news.getImagePath().equals(""))
        Picasso.with(context).load(R.drawable.logo_Def).fit().centerCrop().into(holder.picture);
    else
        Picasso.with(context).load(news.getImagePath()).fit().centerCrop().into(holder.picture);



    holder.date.setText(news.getShortDate());

    if (selectedItem == position)
        holder.itemView.setSelected(true);

}

@Override
public int getItemCount() {
    return newslist.size();
}


public void insert(int position, News data) {
    newslist.add(position - 1, data);
    notifyItemInserted(position);
}

public class MyViewHolder extends RecyclerView.ViewHolder {
    TextView name;
    TextView shortText;
    TextView date;
    ImageView picture;

    public MyViewHolder(View view) {
        super(view);
        this.name=(TextView)view.findViewById(R.id.news_title);
        this.shortText=(TextView)view.findViewById(R.id.news_desc);
        this.picture=(ImageView)view.findViewById(R.id.news_image);
        this.date=(TextView)view.findViewById(R.id.news_date);
    }
}

}

This is my scrolllsitener

  newsList.addOnScrollListener(new RecyclerView.OnScrollListener() {

        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);
            visibleItemCount = newsList.getChildCount();
            totalItemCount = mLayoutManager.getItemCount();
            firstVisibleItem = mLayoutManager.findFirstVisibleItemPosition();
            Log.d("Visibleitem", String.valueOf(visibleItemCount));
            Log.d("totalItem", String.valueOf(totalItemCount));
            Log.d("firstvisibleitem", String.valueOf(firstVisibleItem));
            if (restarting) {
                previousTotal = 0;
                visibleThreshold = 5;

            }
            if (loading) {
                if (totalItemCount > previousTotal) {
                    loading = false;

                    previousTotal = totalItemCount;
                }
            }
            if (!loading && (totalItemCount - visibleItemCount)
                    <= (firstVisibleItem + visibleThreshold)) {
                offset++;
                showlist();
                // Do something

                loading = true;
                restarting = false;
            }
        }
    });

Also if it's meter this funciton is called every time when user scroll to this fragment via this:

  @Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (isVisibleToUser && !areNewsLoaded) {
        listNews = new ArrayList<>();
        offset=0;
        showlist();
        restarting = true;



    }

}

回答1:

I tried solutions posted above but none worked. Helpfully I manage to find some fix. Solution is in 3 magic lines :

 private Parcelable recyclerViewState; 
 recyclerViewState = newsList.getLayoutManager().onSaveInstanceState();
 newsList.getLayoutManager().onRestoreInstanceState(recyclerViewState);

So basically I added 2. line before adding new content to my list and I guess it remember current position and I added 3. line after adding content so I assume this piece of code remember position

回答2:

Try using notifyDataSetChanged() instead of notifyItemInserted().

A new insert method:

public void insert(News data) {
    newslist.add(data);
    notifyDataSetChanged();
}

Also i suggest create method to append all news at one time and use addAll method of ArrayList

回答3:

try something like this ,

first you have to create interface

public interface Update{
public void OnDBUpdate();
 }

then in Main Activity or somewhere add this

public class MainActivity extends AppCompatActivity implements  DialogFragUpdateListener

and create method where you call the Recycler adapter

 public void OnDBUpdate() {
        dbList =helpher.getDataFromDB();
        mAdapter = new RecyclerAdapter(this,dbList);
        mRecyclerView.setAdapter(mAdapter);
    }

and the last step ,, call the method where you need to update recycler

        ((Update) getActivity()).OnDBUpdate();

hope this help :)

来源：https://stackoverflow.com/questions/39819346/recyclerview-scrolling-top-when-loading-new-data