Question

我正在尝试从SD卡中获取mp3文件并将它们放在listview上为什么这段代码无法正常工作时将元素添加到歌曲名称时会搞砸

String[] proj = { MediaStore.Audio.Media._ID,
                  MediaStore.Audio.Media.DATA,
                  MediaStore.Audio.Media.DISPLAY_NAME,
                  MediaStore.Audio.Artists.ARTIST };
Cursor tempCursor = managedQuery(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,
                                 proj,
                                 null,
                                 null,
                                 null);
tempCursor.moveToFirst(); //reset the cursor
int col_index=-1;
int numSongs=tempCursor.getCount();
int currentNum=0;
do{
    col_index = tempCursor.getColumnIndexOrThrow(MediaStore.Audio.Artists.ARTIST);
    List<String> songname = new ArrayList<String>();
    if(tempCursor.moveToNext()){
        songname.add(tempCursor.getString(currentNum+1));
        ArrayAdapter<String> songss = new ArrayAdapter<String>(this, R.id.songs,songname);
        setListAdapter(songss);
    } else{
        return;
    }
    currentNum++;  
}while (tempCursor.moveToNext());

Answer 1

这一行应该在do ... while（）循环之外

List<String> songname = new ArrayList<String>();

作为循环迭代每次songname将在内存中使用新对象定义并且您只获得姓氏。 simillary此代码也在while循环之后

ArrayAdapter<String> songss = new ArrayAdapter<String>(this, R.id.songs,songname);
setListAdapter(songss);

这是完整的代码

String[] proj = { MediaStore.Audio.Media._ID,
                  MediaStore.Audio.Media.DATA,
                  MediaStore.Audio.Media.DISPLAY_NAME,
                  MediaStore.Audio.Artists.ARTIST };
Cursor tempCursor = managedQuery(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,
                                 proj,
                                 null,
                                 null,
                                 null);

int col_index=-1;
int numSongs=tempCursor.getCount();
int currentNum=0;
List<String> songname = new ArrayList<String>();
while (tempCursor.moveToNext())
    col_index = tempCursor.getColumnIndexOrThrow(MediaStore.Audio.Artists.ARTIST);

    songname.add(tempCursor.getString()); // here you need the column index number of song title name only
}

ArrayAdapter<String> songss = new ArrayAdapter<String>(this, R.id.songs,songname);
setListAdapter(songss);

Answer 2

这段代码没有多大意义，你想做什么？

List<String> songNames = new ArrayList<String>();
Cursor c = grabCursorWithSongs();
try {
    while (c.moveToNext()) {
        String songName = c.getString(c.getColumnIndex("song_name"));
        songNames.add(songName);
    }
} finally {
    c.close();
}
ArrayAdapter<String> adapter = new ArrayAdapter<String>(...);
setListAdapter(adapter);

发出向List <string> </string>添加字符串的问题

2 个答案: