java - Cannot handover value from Activity to Repository to pass it into Dao method

Question

I have a vocabulary room-database where words are divided into 4 categories (indicated in respective field of the table).

When the Activity launches, the method getWords() from Dao is triggered with the required argument being passed by WorkActivity

On launching the Activity I get the following error

Cannot create an instance of class space.rodionov.englishwanker.WordViewModel.

Where did I go wrong? Any help is appreciated

In Dao:

@Query("SELECT * FROM word_table WHERE category IN(:filterCategory) ORDER BY RANDOM() LIMIT 4")
    Single<List<Word>> get4words(List<Integer> filterCategory);

In Repository:

public class WordRepository {
    private ArrayList<Integer> categoryFilter;
    private WordDao mWordDao;   
    //other variables
    WordRepository(Application application) {
        WordDatabase db = WordDatabase.getDatabase(application);
        mWordDao = db.WordDao();
        clearFilter();
        setFilter(categoryFilter);
        m4words = mWordDao.get4words(categoryFilter);
    }
    public void clearFilter(){
        categoryFilter.clear();
    }

    public void setFilter(ArrayList<Integer> categoryFilter) {
        this.categoryFilter = categoryFilter;
    }
    

In ViewModel:

private ArrayList<Integer> categoryFilter = new ArrayList<>();
private WordRepository mRepository;
// declaring variables
public WordViewModel(@NonNull Application application) {
    mRepository = new WordRepository(application);
    //declaring
    mRepository.setFilter(categoryFilter);
    m4words = mRepository.get4words();
}
public void clearFilter() {
    categoryFilter.clear();
}
public void setFilter(ArrayList<Integer> categoryFilter) {
    this.categoryFilter = categoryFilter;
}
//other methods

In WorkActivity:

private WordViewModel wordViewModel;
public ArrayList<Integer> categoryFilter = new ArrayList<>();
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        SharedPreferences sharedPreferences = getSharedPreferences("save", MODE_PRIVATE);
        boolean category0 = sharedPreferences.getBoolean("Category0", true);
        boolean category1 = sharedPreferences.getBoolean("Category1", true);
        //other catigories from memory ... 
        //
        wordViewModel = new ViewModelProvider(this,
            ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication()))
            .get(WordViewModel.class);
        wordViewModel.getListLivedata().observe(this, words -> {
            adapter.submitList(words);
        });
        //
        wordViewModel.clearFilter();
        if (category0 == true) {
            categoryFilter.add(0);
            Log.d(TAG, "onCreate: common_words added: called");
        }
        //other categories
        wordViewModel.setFilter(categoryFilter);
        //other methods
        //buildRecyclreVeiw
    }

question from:https://stackoverflow.com/questions/65934955/cannot-handover-value-from-activity-to-repository-to-pass-it-into-dao-method

Answer 1

Answer is I just forgot to initialize ArrayList categoryFilter in Repository.