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当我在我的 ListView 上快速滚动时，我试图让这些字母出现。出于某种原因，出现的字母始终是我的字母表中的第一个字母（空格）。似乎getSectionForPosition()总是返回 0，即使它不应该。下面是我的代码：

活动主机.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".HostActivity" >
    <ListView android:id="@+id/song_list" 
        android:layout_width="fill_parent" 
        android:layout_height="fill_parent"
        android:fastScrollEnabled="true" />
</RelativeLayout>

HostActivity.java

public class HostActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_host);

        loadSongs();
    }

    private void loadSongs() {
        Uri songsUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
        String[] projection = SongCursorAdapter.SONG_COLUMNS;
        String songFilter = MediaStore.Audio.Media.IS_MUSIC + " != 0";
        String orderBy = SongCursorAdapter.ORDERED_BY;
        Cursor songCursor = new CursorLoader(this, songsUri, projection, songFilter, null, orderBy).loadInBackground();

        SongCursorAdapter songsAdapter = new SongCursorAdapter(this, songCursor, 0);
        ListView songView = (ListView) this.findViewById(R.id.song_list);
        songView.setAdapter(songsAdapter);
    }
}

SongCursorAdapter.java

class SongCursorAdapter extends CursorAdapter implements SectionIndexer {
    public final static String[] SONG_COLUMNS = { MediaStore.Audio.Media._ID, MediaStore.Audio.Media.TITLE, MediaStore.Audio.Media.TITLE_KEY, MediaStore.Audio.Media.DATA };
    public final static String ORDERED_BY = MediaStore.Audio.Media.DEFAULT_SORT_ORDER;

    private Context context;
    private AlphabetIndexer indexer;

    SongCursorAdapter(Context context, Cursor c, boolean autoRequery) {
        super(context, c, autoRequery);
        this.context = context;

        setupIndexer(c);
    }

    SongCursorAdapter(Context context, Cursor c, int flags) {
        super(context, c, flags);
        this.context = context;

        setupIndexer(c);
    }

    private void setupIndexer(Cursor c) {
        int sortedByColumn = c.getColumnIndexOrThrow(ORDERED_BY);
        String alphabet = " ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    indexer = new AlphabetIndexer(c, sortedByColumn, alphabet);
    }

    @Override
    public void bindView(View view, Context context, Cursor cursor) {
        // code irrelevant
    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        View view = LayoutInflater.from(context).inflate(R.layout.song_layout, null);
        return view;
    }

    @Override
    public Cursor swapCursor(Cursor c) {
        if (c != null) {
            setupIndexer(c);
        }
        return super.swapCursor(c);
    }

    @Override
    public int getPositionForSection(int section) {
        return indexer.getPositionForSection(section);
    }

    @Override
    public int getSectionForPosition(int position) {
        return indexer.getSectionForPosition(position);
    }

    @Override
    public Object[] getSections() {
        return indexer.getSections();
    }
}

编辑：现在根本没有字母出现。不过，导航栏的行为很奇怪。每次向下滚动时，它都会跳回顶部。

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