当询问用户权限时，ArrayList不是初始化的，但是下次应用重新启动时，它将显示内容

Question

我在片段中请求用户许可（由于该片段中的RecyclerView），但是在给出用户许可后，RecyclerView为空。但是，当我重新启动应用程序时，recyclerView会填充数据。

public class RecyclerViewFragment extends Fragment {

    public RecyclerView songListRecycleView;
    recyclerViewAdapter mAdapter;
    ArrayList<songInfo> songs;

    public void RecyclerViewFragment(){
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.recycler_view_fragment_layout,container,false);

        songs = new ArrayList<>();
        if(getActivity().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE)!= PackageManager.PERMISSION_GRANTED){
            requestStoragePermission();
            //Toast.makeText(getActivity(), "Permission Granted YES", Toast.LENGTH_SHORT).show();
            //songs = getSongArrayList();
            //Log.v("listSize",""+songs.size());
        }else if (getActivity().checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE)==PackageManager.PERMISSION_GRANTED){
            songs = getSongArrayList();
            //Toast.makeText(getContext(), "Permission Granted", Toast.LENGTH_SHORT).show();
        }

        //setting recycler view
        songListRecycleView = view.findViewById(R.id.songListViewId);
        RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getActivity());
        songListRecycleView.setLayoutManager(mLayoutManager);


        return view;
    }

    private static final int MY_PERMISSIONS_REQUEST = 100;
    private void requestStoragePermission(){
        if (ContextCompat.checkSelfPermission(getContext(),
                Manifest.permission.READ_EXTERNAL_STORAGE)
                != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(getActivity(),
                    new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                    MY_PERMISSIONS_REQUEST);
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
        switch (requestCode) {
            case MY_PERMISSIONS_REQUEST: {
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                    songs = getSongArrayList();
                    Toast.makeText(getContext(), "Permission Granted", Toast.LENGTH_SHORT).show();
                    // permission was granted, yay! Do the
                    // file-related task you need to do.
                }
                else {
                    // permission denied, boo! Disable the
                    // functionality that depends on this permission.
                }
                return;
            }
        }
    }


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

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        mAdapter = new recyclerViewAdapter(getActivity(),songs);
        songListRecycleView.setAdapter(mAdapter);
    }

    public ArrayList<songInfo> getSongArrayList(){
        ArrayList<songInfo> songInfos = new ArrayList<songInfo>();
        Cursor cursor = getSongCursor();

        if(cursor!=null){
            Log.v("cursor_NULL","NO");
            Toast.makeText(getActivity(), ""+cursor.getCount(), Toast.LENGTH_SHORT).show();
            int titleIndex = cursor.getColumnIndexOrThrow(MediaStore.Audio.Media.TITLE);
            int dataIndex = cursor.getColumnIndexOrThrow(MediaStore.Audio.Media.DATA);
            songInfo sInfo;
            cursor.moveToFirst();
            for(int i=0;i<cursor.getCount();i++){
                sInfo = new songInfo((String)cursor.getString(titleIndex),(String)cursor.getString(dataIndex));
                songInfos.add(sInfo);
                cursor.moveToNext();
            }
        }else{
            Log.v("cursor_NULL","YES");
        }
        return songInfos;
    }

    public Cursor getSongCursor(){
        try{
            Uri externalUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
            String[] projection = new String[]{
                    MediaStore.Audio.Media.TITLE,
                    MediaStore.Audio.Media.DATA};
            String sortOrder = MediaStore.Audio.Media.TITLE+" ASC";
            Cursor songCursor = getContext().getContentResolver().query(externalUri,projection,null,null,sortOrder);
            Log.v("cursor_length","" + songCursor.getCount());
            return songCursor;
        }catch (Exception e){
            return null;
        }
    }
}

而且我也想知道，首先将内容放入游标，然后将数据插入ArrayList，然后将其用于RecyclerView Adapter是个好主意。如果我直接在Adapter中使用游标，或者在Adapater中使用ArrayList会有什么性能上的区别。