Room数据库预填充数据不显示问题解析与解决方案

@Database(entities = {Note.class}, version = 1)
public abstract class NoteDatabase extends RoomDatabase {

    private static NoteDatabase instance;

    public abstract NoteDao noteDao();

    public static synchronized NoteDatabase getInstance(Context context){
        if(instance == null){
            instance = Room.databaseBuilder(context.getApplicationContext(),
                    NoteDatabase.class, "note_database")
                    .fallbackToDestructiveMigration()
                    .addCallback(roomCallback) // 添加回调
                    .build();
        }
        return instance;
    }

    private static RoomDatabase.Callback roomCallback = new RoomDatabase.Callback(){
        @Override
        public void onCreate(@NonNull SupportSQLiteDatabase db) {
            super.onCreate(db);
            // 数据库首次创建时执行数据填充
            new PopulateDbAsyncTask(instance).execute();
        }
    };

    private static class PopulateDbAsyncTask extends AsyncTask<Void, Void, Void>{
        private NoteDao noteDao;

        public PopulateDbAsyncTask(NoteDatabase db){
            noteDao = db.noteDao();
        }

        @Override
        protected Void doInBackground(Void... voids) {
            // 插入预设数据
            noteDao.insert(new Note("Title 1", "Description 1", 1));
            noteDao.insert(new Note("Title 2", "Description 2", 2));
            noteDao.insert(new Note("Title 3", "Description 3", 3));
            return null;
        }
    }
}

private static class PopulateDbAsyncTask extends AsyncTask<Void, Void, Void>{
    private NoteDao noteDao;

    public PopulateDbAsyncTask(NoteDatabase db){
        noteDao = db.noteDao();
    }

    @Override
    protected Void doInBackground(Void... voids) {
        // 检查数据库是否已存在数据
        // 注意：LiveData查询不能直接在AsyncTask中执行，需要同步查询
        // 假设NoteDao有一个同步方法来获取数据计数
        // 例如：@Query("SELECT COUNT(*) FROM note_table") int getNoteCount();
        // if (noteDao.getNoteCount() == 0) {
            noteDao.insert(new Note("Title 1", "Description 1", 1));
            noteDao.insert(new Note("Title 2", "Description 2", 2));
            noteDao.insert(new Note("Title 3", "Description 3", 3));
        // }
        return null;
    }
}