我正在开发一个音乐播放器。所以我需要在自定义ListView中加载歌曲列表，该ListView有一个ImageView和两个textView。它的性能太慢，所以我在谷歌搜索，我找到了一个解决方案，说“在后台使用AsyncTasks和加载listView”。但是listview的表现还是太慢了。请帮我提高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，并且它位于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;
}
}
答案 0 :(得分：1)
不要使用AsyncTask但需要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);
}
}
答案 1 :(得分：0)
使用AsyncTask加载列表视图数据的想法意味着仅为特定项目加载数据。您可能知道ListView只会询问他的适配器在屏幕上可见的项目（加上可见区域的上方和下方）。一旦您的适配器不需要一次提供所有数据，您可以根据需要加载它 以下只是可能实施的一个概要：
// We need a queue to run only one AsyncTask
// How to deal with queue you may find here
// http://developer.android.com/reference/java/util/concurrent/BlockingQueue.html
BlockingQueue loadViewQueue;
@Override
public int getCount() {
return countOfYourData;
}
@Override
public View getView( int position, View convertView, ViewGroup parent ) {
if( convertView == null ) {
convertView = LayoutInflater.from(getContext()).inflace( yourresId, parent, false );
}
// if you don't use ViewHolder patter you may store position as shown below
// otherwise create appropriate field in ViewHolder class and store position there
convertView.setTag(position);
loadViewQueue.put(convertView);
}
class LoadingAsyncTask extends AsyncTask< View, Object, Void > {
Integer position;
@Override
protected Void doInBackground( View... params ) {
while(true) {
View view = loadViewQueue.take();
position = ( Integer )view.getTag();
Data data = loadDataFromDb(position);
publishProgress( position, data );
}
return null;
}
@Override
protected void onProgressUpdate( Object result ) {
applyDataToListItem((Integer)result[0], (Data)result[1]);
}
}
当然队列必须同步并添加错误检查。