My Recycleview display list and complete list only intermittently displays the last item I add to my ArrayList

Question

My recycleview in android v7 displays the list sometimes. It doesn't display the list when I restart the app from my phone. It can count all the audio files but when I set it to textview, it just displays only the last data added in the list view. My code is below. Can someone tell me how to display Recycle list data concurrently with using the Androi's new AsyncListUtil.

//MainActivity.java
package fragment.dev.concurrentmedia;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

public class MainActivity extends AppCompatActivity {

    RecyclerView recyclerView;
    RecAdapter adapter;

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

        recyclerView = (RecyclerView) findViewById (R.id.recycleview);
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager (getApplicationContext ());
        recyclerView.setLayoutManager (layoutManager);
        recyclerView.setItemAnimator (new DefaultItemAnimator ());
        recyclerView.setHasFixedSize (true);

        adapter = new RecAdapter (getApplicationContext ());
        recyclerView.setAdapter (adapter);
    }
}

//AudioSync.java
package fragment.dev.concurrentmedia;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.AsyncTask;
import android.provider.MediaStore;
import java.util.ArrayList;
import java.util.List;
/**
 * Created by Jagdish on 6/19/2016.
 */
public class AudioSync extends AsyncTask<Context, Void, List<AudioModel>> {
    public Response delegate = null;
    private String selection;
    private Uri uri;
    private Cursor cursor;
    @Override
    protected List<AudioModel> doInBackground (Context... params) {
        List<AudioModel> modelList = new ArrayList<> ();
        AudioModel model = new AudioModel ();
        try {
            selection = MediaStore.Audio.Media.IS_MUSIC + "!=0";
            uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
            String projection[] = {MediaStore.Audio.Media.DATA, MediaStore.Audio.Media.DISPLAY_NAME, MediaStore.Audio.Media.DURATION};
            cursor = params[0].getContentResolver ().query (uri, projection, selection, null, null);
            cursor.moveToFirst ();
            int i = 0;
            do {
                model.setPath (cursor.getString (cursor.getColumnIndexOrThrow (MediaStore.Audio.Media.DATA)));
                model.setDisplayName (cursor.getString (cursor.getColumnIndexOrThrow (MediaStore.Audio.Media.DISPLAY_NAME)));
                model.setDuration (cursor.getString (cursor.getColumnIndexOrThrow (MediaStore.Audio.Media.DURATION)));
                modelList.add (model);
            } while (cursor.moveToNext ());
            return modelList;
        } catch (Exception e) {
            L.l ("EXCEPTION", e.getStackTrace ());
            return modelList;
        }
    }
    @Override
    protected void onPostExecute (List<AudioModel> audioModels) {
        delegate.processFinish (audioModels);
    }
    public interface Response {
        void processFinish (List<AudioModel> output);
    }
}

//RecAdapter.java
package fragment.dev.concurrentmedia;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Jagdish on 6/19/2016.
 */
public class RecAdapter extends RecyclerView.Adapter<RecAdapter.MyViewHolder> implements AudioSync.Response {
    public List<AudioModel> models = new ArrayList<> ();

    public RecAdapter (Context context) {
        AudioSync sync = new AudioSync ();
        sync.delegate = this;
        sync.execute (context);
    }

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

    @Override
    public void onBindViewHolder (MyViewHolder holder, int position) {
        AudioModel audioModel = models.get (position);
        holder.txtName.setText (audioModel.getDisplayName ());
        holder.txtDuration.setText (audioModel.getDuration ());
    }

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

    @Override
    public void processFinish (List<AudioModel> output) {
        for (int i = 0; i < output.size (); i++) {
            models.add (output.get (i));
        }
    }

    public class MyViewHolder extends RecyclerView.ViewHolder {
        public TextView txtName;
        public TextView txtDuration;

        public MyViewHolder (View itemView) {
            super (itemView);
            txtName = (TextView) itemView.findViewById (R.id.txtName);
            txtDuration = (TextView) itemView.findViewById (R.id.txtDuration);
        }
    }
}

//AudioModel.java
package fragment.dev.concurrentmedia;

/**
 * Created by Jagdish on 6/19/2016.
 */
public class AudioModel {
    private String displayName;
    private String duration;
    private String path;

    public String getDisplayName () {
        return displayName;
    }

    public void setDisplayName (String displayName) {
        this.displayName = displayName;
    }

    public String getDuration () {
        return duration;
    }

    public void setDuration (String duration) {
        this.duration = duration;
    }

    public String getPath () {
        return path;
    }

    public void setPath (String path) {
        this.path = path;
    }
}

//L.java
package fragment.dev.concurrentmedia;

import android.util.Log;

/**
 * Created by Jagdish on 6/19/2016.
 */
public class L {
    public static void l (String detail, Object msg) {
        Log.d ("JR", detail + " : " + msg);
    }
}

Answer 1

I think the best thing here is to move the async task out from the adapter and start it in the activity's onCreate callback. As soon as the async task completes, you create the adapter and provide it to the recyclerview.