I have a RecyclerView in a Fragment. Also I have an AsyncTask which updates items of RecyclerView from background thread. The problem is when I rotate the device (or cause any other configuration change), the AsyncTask cannot update views.

Here you can see the simplified code:

HomeFragment:

public class HomeFragment extends Fragment {

    public HomeFragment() {
    }

    public static HomeFragment newInstance() {
        return new HomeFragment();
    }

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_home, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        RecyclerView mRecyclerView = requireView().findViewById(R.id.recyclerview);
        Activity activity = requireActivity();
        ArrayList<String> items = new ArrayList<>(Arrays.asList("Item1", "Item2", "Item3"));
        ListAdapter adapter = new ListAdapter(activity, items);
        mRecyclerView.setAdapter(adapter);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(activity));
    }
}

The adapter of RecyclerView and its inner AsyncTask class:

public class ListAdapter extends RecyclerView.Adapter<ListAdapter.ViewHolder> {

    private final ArrayList<String> items;
    private final LayoutInflater mInflater;
    private RecyclerView mRecyclerView;

    public ListAdapter(Context context, ArrayList<String> items) {
        mInflater = LayoutInflater.from(context);
        this.items = items;
    }

    @Override
    public void onAttachedToRecyclerView(@NonNull RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);
        mRecyclerView = recyclerView;
    }

    @NonNull
    @Override
    public ListAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View mItemView = mInflater.inflate(R.layout.item, parent, false);
        return new ViewHolder(mItemView, this);
    }

    @Override
    public void onBindViewHolder(@NonNull ListAdapter.ViewHolder holder, int position) {
        holder.name.setText(items.get(position));
    }

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

    public class ViewHolder extends RecyclerView.ViewHolder {
        final ListAdapter mAdapter;
        final TextView name;

        public ViewHolder(@NonNull View itemView, ListAdapter mAdapter) {
            super(itemView);
            this.mAdapter = mAdapter;
            this.name = itemView.findViewById(R.id.file_name);
            itemView.setOnClickListener(v -> {
                Task task = new Task();
                task.execute();
            });
        }
    }

    class Task extends AsyncTask<Void, Integer, Void> {

        @Override
        protected void onProgressUpdate(Integer... values) {
            mRecyclerView.post(() ->
                    ((ViewHolder) Objects.requireNonNull(mRecyclerView.findViewHolderForLayoutPosition(0))).
                            name.setText(String.valueOf(values[0])));
            mRecyclerView.invalidate();
        }

        @Override
        protected Void doInBackground(Void... voids) {
            for (int i = 0; i <= 30; i  ) {
                publishProgress(i);
                SystemClock.sleep(500);
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void unused) {
            ((ViewHolder) Objects.requireNonNull(mRecyclerView.findViewHolderForLayoutPosition(0))).name.setText("task is finished");
        }
    }
}

As you can see I used mRecyclerView.post() method to avoid touching views from non UI thread. How I can update items after rotating the device?

What I tried before:

• changing data set of adapter and calling notifyDataSetChanged()
• creating a method in Fragment for updating items and calling it from AsyncTask
• resetting adapter for RecyclerView
• ...

CodePudding user response：

You can use below code for update recycler view in screen rotation.

@Override
public void onConfigurationChanged(@NonNull Configuration newConfig) {

    super.onConfigurationChanged(newConfig);

    if(adapter!=null){
        adapter.notifyDataSetChanged();
    }
}

Call setRetainInstance(true) in either of onCreate(), onCreateView() or onActivityCreated() methods.

CodePudding user response：

Async task by default work on background thread, we cannot update our ui from background thread it's used for intensive works such as network calls etc. Please try running a

runOnUiThread(new Runnable() {
        @Override
        public void run() {
            // WORK on UI thread here
        }
    });

statement in your async task's onPostExecute method because it indicates your background processing is completed. put code that update views inside this run() method