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从音乐的标题中，尝试得到对应的艺术家、专辑名称和专辑封面。我使用LoaderManager和CursorLoader。创建 Activity 后，我用getLoaderManager().initLoader(1, null, this). 这是我的加载器的代码：

在创建加载器时

static final String[] PLAYER_SUMMARY_PROJECTION = { MediaStore.Audio.Media._ID, MediaStore.Audio.Media.TITLE, MediaStore.Audio.Media.ARTIST, MediaStore.Audio.Media.ALBUM};
    static final String[] PLAYER_COVER_SUMMARY_PROJECTION = { MediaStore.Audio.Albums.ALBUM_ID, MediaStore.Audio.Albums.ALBUM_ART, MediaStore.Audio.Albums.ALBUM};

    public Loader<Cursor> onCreateLoader(int id, Bundle arg1) {
        CursorLoader loader;    

    if(id==1){

        String where = android.provider.MediaStore.Audio.Media.TITLE
                  + "=?";
        String whereVal[] = {dataalbumsTrackRequested};
        loader = new CursorLoader(getActivity(), MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,  
        PLAYER_SUMMARY_PROJECTION, where, whereVal,null); }

    else{

         String where2 = android.provider.MediaStore.Audio.Media.ALBUM
          + "=?";
         String whereVal2[] = {album};
         loader = new CursorLoader(getActivity(), MediaStore.Audio.Albums.EXTERNAL_CONTENT_URI,  
         PLAYER_COVER_SUMMARY_PROJECTION, where2, whereVal2,null);  }

    return loader;

    }

加载完成

public void onLoadFinished(Loader<Cursor> loader, Cursor cursor) {

     if(loader.getId()==1){

     //Fill the text view with their value

     //Set Title
     String title =cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.TITLE));
     TextView titleView = (TextView)getView().findViewById(R.id.musicTitle);
     titleView.setText(title);

     //Set Artist
     String artist =cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ARTIST));
     TextView artistView = (TextView)getView().findViewById(R.id.artistName);
     if (artist.equals("<unknown>")){artistView.setText(R.string.unknown_album);}
     else { artistView.setText(artist);}

     //Set Album
     album =cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ALBUM));
     TextView albumView = (TextView)getView().findViewById(R.id.albumTitle);
     if (album.equals("<unknown>")){albumView.setText(R.string.unknown_album);}
     else { albumView.setText(album);}

             }

    else {   


     ImageView coverView = (ImageView)getView().findViewById(R.id.playerCoverView);

     if (cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Albums.ALBUM_ART)).equals(null)){
            //if no cover returned, display the by default (empty) cover
            coverView.setImageResource(R.drawable.listcoverthumbnail);}

     else{
            Bitmap coverImage = BitmapFactory.decodeFile(cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Albums.ALBUM_ART)));
                    coverView.setImageBitmap(coverImage);}

      getLoaderManager().initLoader(2, null, this);
  }

该变量album是为整个类定义的，dataalbumsTrackRequested是一个字符串，等于所需专辑的标题。

该应用程序崩溃，我得到：

06-19 16:21:42.720: E/AndroidRuntime(6516): Caused by: android.database.sqlite.SQLiteException: no such column: album_art: , while compiling: SELECT album_id, album_art, album FROM audio WHERE (album=?)

如果我删除了第二个加载器（Id=2），那么封面当然不会显示，但应用程序不会崩溃。所以问题来自第二个Loader。

我究竟做错了什么 ？我确信这个专栏album_art存在，因为我已经在我的另一个应用程序中获得了这样的封面。但是在这里，我找不到错误的来源。是因为我使用了多个 Loaders 吗？

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1 回答 1

2

好的，问题解决了。

1）在第二个加载器中，我使用的是MediaStore.Audio.Media.ALBUM而不是MediaStore.Audio.albums.ALBUM

2）我的预测是PLAYER_COVER_SUMMARY_PROJECTION = { MediaStore.Audio.Albums.ALBUM_ID, MediaStore.Audio.Albums.ALBUM_ART, MediaStore.Audio.Albums.ALBUM}

代替PLAYER_COVER_SUMMARY_PROJECTION = { MediaStore.Audio.Albums._ID, MediaStore.Audio.Albums.ALBUM_ART, MediaStore.Audio.Albums.ALBUM};

然后，如果您收到错误06-19 19:29:18.115: E/AndroidRuntime(22943): android.database.CursorIndexOutOfBoundsException: Index -1 requested, with a size of 1，我用cursor.move(cursor.getPosition()+2)in OnLoadFinishedof the解决了它Loader。这是一个可怕的黑客，但它的工作原理。

显然我不是唯一一个遇到这个问题的人（例如，参见这篇文章），但我已经以另一种方式解决了它。

于 2012-06-19T17:33:44.497 回答