房间。添加到收藏夹。调用更新时出错

Question

帮助我了解我在做什么错。片段中有一个项目列表。单击将打开一个具有完整描述的片段，并且有一个“添加到收藏夹”按钮。当我尝试致电更新model.update (data);时引发错误

Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'void avocado.droid.ptitsami.room.DataDao.update(avocado.droid.ptitsami.room.Data)' on a null object reference
at avocado.droid.ptitsami.room.DataRepository$updateAsyncTask.doInBackground(DataRepository.java:54)
at avocado.droid.ptitsami.room.DataRepository$updateAsyncTask.doInBackground(DataRepository.java:44)
at android.os.AsyncTask$2.call(AsyncTask.java:295)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)`

但是模型不为空。在onChanged方法中，数据已成功设置。

DataDao

     @Query("SELECT * FROM Data WHERE id = :id")
LiveData<Data> getById(int id);

@Update
void update(Data data);

DataRepository

     LiveData<Data> getById(int id) {
    return db.getDatabase().dataDao().getById(id);
}

void update(Data data) {
    new updateAsyncTask(dataDao).execute(data);
}

private static class updateAsyncTask extends AsyncTask<Data, Void, Void> {

    private DataDao mAsyncTaskDao;

    updateAsyncTask(DataDao dao) {
        mAsyncTaskDao = dao;
    }

    @Override
    protected Void doInBackground(final Data... params) {
        mAsyncTaskDao.update(params[0]);
        return null;
    }
}

ViewModel

    public class DataViewModel extends AndroidViewModel {
    LiveData<Data> currentData;
    DataRepository repository;


    public DataViewModel(@NonNull Application application, final int dataId) {
        super(application);
        int verseId = dataId;
        repository = new DataRepository(application);
        currentData = repository.getById(verseId);
    }

    public LiveData<Data> getById() {
        return currentData;
    }

   public void update(Data data) {
        repository.update(data);
    }


    public static class ModelFactory extends ViewModelProvider.NewInstanceFactory {

        @NonNull
        private final Application application;
        private final int dataId;
        private final DataRepository repository;

        public ModelFactory(@NonNull Application application, int id) {
            super();
            this.application = application;
            this.dataId = id;
            repository = new DataRepository(application);
        }

        @NonNull
        @Override
        public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
            if (modelClass == DataViewModel.class) {
                return (T) new DataViewModel(application, dataId);
            }
            return null;
        }
    }
}

以及发生一切的片段方法

final DataViewModel.ModelFactory factory = new DataViewModel.ModelFactory(
        getActivity().getApplication(), getArguments().getInt(KEY_DATA_ID));

final DataViewModel model = ViewModelProviders.of(this, factory)
        .get(DataViewModel.class);

model.getById().observe(this, new Observer<Data>() {
    @Override
    public void onChanged(final Data data) {
        tvTitle.setText(data.getTitle());

        favorite = data.getFavorite();
        if (favorite == 0) {
            ivLike.setImageResource(R.drawable.heart_outline);
        } else {
            ivLike.setImageResource(R.drawable.heart_ok);
        }

        ivLike.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (favorite == 0) {
                    favorite = 1;

                    model.update(data); 
                    ivLike.setImageResource(R.drawable.heart_ok);
                    anim = AnimationUtils.loadAnimation(getActivity(), R.anim.my_anim);
                    ivLike.startAnimation(anim);

                } else {

                }