当我不修改数组时出现 ConcurrentModificationException？

Question

我得到 java.util.ConcurrentModificationException，我不知道为什么。

在 Logcat 中它指向此代码，但我没有看到任何可能导致 ConcurrentModificationException 的内容。

 private void initRecyclerView() {
    Main.musicList = Main.songs.songs;
    Log.d(TAG, "Main.musicList: " + String.valueOf(Main.musicList));
    if ((Main.musicList != null) && (!Main.musicList.isEmpty())) {
        // Connects the song list to an adapter
        // (Creates several Layouts from the song list)
        allSongsAdapter = new AllSongsAdapter(getActivity(), Main.musicList);

        final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());

        recyclerViewSongs.setLayoutManager(linearLayoutManager);
        recyclerViewSongs.setHasFixedSize(true);
        recyclerViewSongs.setAdapter(allSongsAdapter);
   }
}

Main.musicList 是一个公共静态 ArrayList musicList = null;在另一个班级。

而Main.songs.songs是一个公共的ArrayListsongs = null;在我的课堂上，我获取设备上的所有歌曲并用它们填充数组列表。

在 onDestroy 中我调用：

musicList = null;

编辑

好的，我发现了问题，当我不调用 onDestroy musicList = null 时，没有 ConcurrentModificationException。

但是我如何在 onDestroy 中取消引用一个数组列表，以便它可以被垃圾收集？

编辑

所以问题不在于 onDestroy 调用，当我打开应用程序并且我的数组列表中填充了所有歌曲时发生错误，然后我关闭应用程序并重新打开它，然后引发异常。

我如何填充歌曲数组

   songs = new ArrayList<>();

   // Columns retrieved from the system database (MediaStore.Audio.Media).
    String[] projection1 = {
            SONG_ID,
            SONG_TITLE,
            SONG_ARTIST,
            SONG_ALBUMID,
            SONG_ALBUM,
            SONG_FILEPATH,
            SONG_DURATION,
            SONG_YEAR,
    };
  // Limits results to only show MUSIC files.
    // It's a SQL "WHERE" clause - it becomes `WHERE IS_MUSIC NOT EQUALS ZERO`.
    final String musicsOnly = SONG_IS_MUSIC + "!=0";

    // Querying the Media DATABASE.
    cursor = resolver.query(musicUri, projection1, musicsOnly, null, null);
    try {
        if (cursor != null && cursor.moveToFirst()) {
            do {

                // Creating a SONG from the VALUES in each column.
                Song song = new Song(cursor.getLong(cursor.getColumnIndexOrThrow(SONG_ID)),
                        cursor.getString(cursor.getColumnIndexOrThrow(SONG_FILEPATH)));

                song.setTitle(cursor.getString(cursor.getColumnIndexOrThrow(SONG_TITLE)));
                song.setArtist(cursor.getString(cursor.getColumnIndexOrThrow(SONG_ARTIST)));
                song.setAlbumID(cursor.getLong(cursor.getColumnIndexOrThrow(SONG_ALBUMID)));
                song.setAlbum(cursor.getString(cursor.getColumnIndexOrThrow(SONG_ALBUM)));
                song.setDuration(cursor.getLong(cursor.getColumnIndexOrThrow(SONG_DURATION)));
                song.setYear(cursor.getInt(cursor.getColumnIndexOrThrow(SONG_YEAR)));

                // Using the previously created maps to add the current song GENRE.
                String currentGenreID = songIdToGenreIdMap.get(Long.toString(song.getId()));
                String currentGenreName = genreIdToGenreNameMap.get(currentGenreID);
                song.setGenre(currentGenreName);

                // Adding the Song to the global array list 'songs'.
                songs.add(song);
            } while (cursor.moveToNext());
        }
    }catch (Exception e){
        // Exception caught because no songs were found.
        Log.e(TAG, "Exception caught because no songs were found!", e);
        throw new Exception();
    }finally {
        if (cursor != null ){
            cursor.close();
        }
    }

Answer 1

这是一种高级方法，可以让 GC 正确清除您的内存。

在您的 Activity 类中定义成员：

private List<Song> mMySongs;

在onCreate方法中，你初始化RecyclerView，然后将歌曲读入数组：

// getSongs is your models method where you read the songs and return them as array
mMySongs = getSongs();
// Enter code to create the adapter and set it for RecyclerView

现在你使用的是强引用而不是静态引用，当你的Activity被销毁时，GC可以清理内存，当你重新启动Activity时它会再次查询歌曲。