java - 即使在 AsyncTask 中，ListView 性能也太慢

Question

我正在开发音乐播放器。所以我需要在一个自定义 ListView 中加载歌曲列表，它有一个 ImageView 和两个 textView。它的性能太慢了，所以我在谷歌中搜索并找到了一个解决方案，上面写着“使用 AsyncTasks 并在后台加载 listView”。但是listview的性能还是太慢了。请帮助我提高 ListView 的性能。这是我的代码:

此代码通过从 song_database 获取值来加载自定义 ArrayList，它位于 Activity 类中。

private ArrayList getListData() {
    ArrayList results = new ArrayList();
    Song Data = new Song();
    Database_Song db = new Database_Song(this);
    String data = db.getData();
        StringTokenizer token = new StringTokenizer(data,";");

        while(token.hasMoreTokens())
        {
            String dataPart = token.nextToken();
            StringTokenizer tokenPart = new StringTokenizer(dataPart,"|");
            Data = new Song();
            Data.setSongTitle(tokenPart.nextToken());
            mediaInfo.setDataSource(tokenPart.nextToken());

            if (mediaInfo.getEmbeddedPicture() != null){
                byte[] img = mediaInfo.getEmbeddedPicture();
                Data.setImage((BitmapFactory.decodeByteArray(img, 0,img.length)));
            }
            else
                Data.setImage(BitmapFactory.decodeResource(this.getResources(), R.drawable.album_art));

            Data.setAlbumName(tokenPart.nextToken());
            results.add(Data);
        }

        return results;
}

这是我的 AsyncTasks 类，它是 Activity 类的内部类。

private class LoadListTask extends AsyncTask<String, Void, Integer> {
    ArrayList Song_details;
    protected void onPreExecute() {

    }

    protected Integer doInBackground(String... params) {
        Song_details = getListData();
        return 0;
    }

    protected void onPostExecute(Integer result) {
        adapter = new CustomListAdapter_Song(cont, Song_details);
        lv_song.setAdapter(adapter);

        if (result == 0) {
            adapter.notifyDataSetChanged();
         }
    }
}

这是我的适配器类

public class CustomListAdapter_Song extends BaseAdapter{

private ArrayList<Song> listData;
private LayoutInflater layoutInflater;
private ArrayList<Song> arraylist;
private int lastPosition = -1;

public CustomListAdapter_Song(Context context, ArrayList<Song> listData) {
    this.listData = listData;
    layoutInflater = LayoutInflater.from(context);
    this.arraylist = new ArrayList<Song>();
    this.arraylist.addAll(listData);
}

@Override
public int getCount() {
    return listData.size();
}

@Override
public Object getItem(int position) {
    return listData.get(position);
}

@Override
public long getItemId(int position) {
    return position;
}

public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
        convertView = layoutInflater.inflate(R.layout.listview_item_row_for_data, null);
        holder = new ViewHolder();
        holder.songName = (TextView) convertView.findViewById(R.id.Song_songTitle);
        holder.albumName = (TextView) convertView.findViewById(R.id.Song_AlbumName);
        holder.songImage = (ImageView) convertView.findViewById(R.id.Song_AlbumImage);
        convertView.setTag(holder);

    } else {
        holder = (ViewHolder) convertView.getTag();
    }

    holder.songName.setText(listData.get(position).getSongTitle());
    holder.albumName.setText(listData.get(position).getAlbumName());
    holder.songImage.setImageBitmap((listData.get(position).getImage()));
    View view = convertView;
    Animation animation = AnimationUtils.loadAnimation(view.getContext(), (position > lastPosition) ? R.anim.up_from_bottom : R.anim.down_from_top);
    view.startAnimation(animation);
    lastPosition = position;

    return convertView;
}

static class ViewHolder {
    TextView songName;
    TextView albumName;
    ImageView songImage;
}   

Answer 1

不要使用 AsyncTask 但你需要 CursorLoader

public class SongsFragment extends ListFragment implements LoaderManager.LoaderCallbacks<Cursor>
{
    SongAdapter adapter;

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

    @Override
    public void onCreate( Bundle savedInstanceState )
    {
        super.onCreate(savedInstanceState);
        adapter = new SongAdapter(getActivity(), null);
        setListAdapter(adapter);
        getLoaderManager().initLoader(0, null, this);

    }

    private class SongAdapter extends CursorAdapter
    {
        Uri sArtworkUri = Uri.parse("content://media/external/audio/albumart");

        public SongAdapter( Context context , Cursor c )
        {
            super(context , c , true);
        }

        @Override
        public View getView( int position , View convertView , ViewGroup parent )
        {
            View v;
            Cursor cursor = (Cursor) getItem(position);
            if (convertView == null)
            {
                v = newView(mContext, cursor, parent);
            }
            else
            {
                v = convertView;
            }
            bindView(v, mContext, cursor);
            return v;
        }

        @Override
        public void bindView( View view , Context context , Cursor cursor )
        {
            ViewHolder holder = (ViewHolder) view.getTag();
            holder.songNameTextView.setText(cursor.getString(2));
            holder.artistTextView.setText(cursor.getString(1));
            Uri albumArtUri = ContentUris.withAppendedId(sArtworkUri, cursor.getLong(3));
            Picasso.with(getActivity()).load(albumArtUri).error(R.drawable.placeholder).placeholder(R.drawable.placeholder).into(holder.albumImageView);
        }

        @Override
        public View newView( Context context , Cursor cursor , ViewGroup parent )
        {
            View view = LayoutInflater.from(context).inflate(R.layout.row_song, parent, false);
            ViewHolder holder = new ViewHolder();
            holder.albumImageView = (ImageView) view.findViewById(R.id.albumImg);
            holder.songNameTextView = (TextView) view.findViewById(R.id.songNameTxtView);
            holder.artistTextView = (TextView) view.findViewById(R.id.artistNameTxtView);
            view.setTag(holder);
            return view;
        }
    }

    private static class ViewHolder
    {
        public ImageView    albumImageView;
        public TextView     artistTextView;
        public TextView     songNameTextView;
    }

    @Override
    public Loader<Cursor> onCreateLoader( int arg0 , Bundle arg1 )
    {
        String[] projection = { MediaStore.Audio.Media._ID, MediaStore.Audio.Media.ARTIST, MediaStore.Audio.Media.TITLE, MediaStore.Audio.Media.ALBUM_ID };
        String selection = MediaStore.Audio.Media.IS_MUSIC + " != 0";
        return new CursorLoader(getActivity(), MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, projection, selection, null, null);
    }

    @Override
    public void onLoadFinished( Loader<Cursor> arg0 , Cursor data )
    {
        adapter.swapCursor(data);
    }

    @Override
    public void onLoaderReset( Loader<Cursor> arg0 )
    {
        adapter.swapCursor(null);
    }
}