how to stop receiving waiting answers from livedata observe Room

Question

I'm dealing with something that I don't understand at all.

If I delete the observer before updating my Room database and then put the observer back on, I have notifications for each update, and the recyclerview is updated as many times.

My partial code:

public class ArticlesListFragment extends Fragment {
    private LiveData<List<Article>> mLDgetAllArticle;
    private long mClistId;
    private ArrayList<Article> mArticles;

    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        this.mLDgetAllArticle = this.articleViewModel.getAllArticle(mclistId);
        this.setArticlesObserver();
        ...
    }
    private void setArticlesObserver() {
        if (this.mLDgetAllArticle != null && !this.mLDgetAllArticle.hasObservers())
            this.mLDgetAllArticle.observe(getViewLifecycleOwner(), this::updateArticlesList);
    }

    private void updateArticlesList(List<Article> articles) {
        this.mArticles = new ArrayList<>(articles);
        this.mArticlesRecyclerViewAdapter.setAdapterDatas(this.mArticles);
    }

    private void removeArticlesObserver() {
        if (this.mLDgetAllArticle != null && this.mLDgetAllArticle.hasObservers())
            this.mLDgetAllArticle.removeObservers(getViewLifecycleOwner());
    }
    private void updateArticle(Article article) {
        this.articleViewModel.updateArticle(article);
    }
    ...
}

Everything is fine so far.

But, elsewhere, I have to update all my Articles, like:

for (int i = 0; i < this.mArticles.size(); i++) {
    this.mArticles.get(i).setOrd(i);
    this.updateArticle(this.mArticles.get(i));
}

Also, I thought I should delete the observer before, and put it back later:

this.removeArticlesObserver();
for (int i = 0; i < this.mArticles.size(); i++) {
    this.mArticles.get(i).setOrd(i);
    this.updateArticle(this.mArticles.get(i));
}
this.setArticlesObserver();

but I still get after all the updates notifications. updateArticlesList is called as many times as there were updateArticles, after setArticlesObserver.

What am I missing?

Is there any way to flush all that waiting results before setting observer again?

ViewModelFactory.java:

public class ViewModelFactory implements ViewModelProvider.Factory {
    private final ArticleDataRepository articleDataSource;
    
    private final Executor executor;
    private static volatile ViewModelFactory factory;

    public static ViewModelFactory getInstance(Context context) {
        if (factory == null) {
            synchronized (ViewModelFactory.class) {
                if (factory == null) {
                    factory = new ViewModelFactory(context);
                }
            }
        }
        return factory;
    }

    private ViewModelFactory(Context context) {
        getDB database = getDB.getInstance(context);
        this.articleDataSource = new ArticleDataRepository(database.articleDao());
        this.executor = Executors.newSingleThreadExecutor();
    }

    @Override
    @NotNull
    public <T extends ViewModel>  T create(Class<T> modelClass) {
        if (modelClass.isAssignableFrom(ArticleViewModel.class)) {
            return (T) new ArticleViewModel(articleDataSource, executor);
        }
        throw new IllegalArgumentException("Unknown ViewModel class");
    }
}

ArticleViewModel.java:

public class ArticleViewModel extends ViewModel {
    private final ArticleDataRepository articleDataSource;
    private final Executor executor;
    public ArticleViewModel(
            ArticleDataRepository articleDataSource,
            Executor executor
    ) {
        this.articleDataSource = articleDataSource;
        this.executor = executor;
    }
    public LiveData<List<Article>> getAllArticle(long clistId) {
        return articleDataSource.getAll(clistId);
    }
}

ArticleDataRepository:

public class ArticleDataRepository {
    private final ArticleDao articleDao;

    public ArticleDataRepository(ArticleDao articleDao) {
        this.articleDao = articleDao;
    }

    public LiveData<List<Article>> getAll(long clistId) {
        return this.articleDao.getAll(clistId);
    }
}

I used this documentation

Answer 1

I took two steps to solve my problem:

1. I'm updating all the articles instead of doing a part one I didn't know I could do

   @Update(onConflict = OnConflictStrategy.REPLACE) void updateAll(ArrayList articles);

   for (int i = 0; i < this.mArticles.size(); i++) { this.mArticles.get(i).setOrd(i); this.updateArticle(this.mArticles.get(i)); }

becomes:

for (int i = 0; i < this.mArticles.size(); i++) {
    this.mArticles.get(i).setOrd(i);
}
this.updateAllArticles(this.mArticles);

2. I put a flag to launch the notifyDataSetChanged() only during specific events and not each time the data is updated.