Cannot create an instance of ViewModel class (Unable to start activity ComponentInfo)

Question

I am using MVVM, Retrofit, LiveData in my project but I get this error before that I saw these links

• Cannot create an instance of custom ViewModel
• Cannot create an instance of class ViewModel

Error

java.lang.RuntimeException:       
Unable to start activity ComponentInfo{ir.orangehat.movieinfo/ir.orangehat.movieinfo.application.home.HomeActivity}: java.lang.RuntimeException:

Cannot create an instance of class ir.orangehat.movieinfo.application.home.HomeViewModel

This is my ViewModel and I think the problem is in my constructor

public class HomeViewModel extends AndroidViewModel {

private MovieRepository movieRepository;

public HomeViewModel(@NonNull Application application, Context context, LifecycleOwner lifecycleOwner) {
    super(application);
    movieRepository = new MovieRepository(lifecycleOwner, context);
}

LiveData<List<Movie>> getMovies() {
    return movieRepository.getMovies();
}}

Repository

public class MovieRepository extends BaseRepository {

private LifecycleOwner lifecycleOwner;
private MovieApi movieApi;
private MovieDatabaseHelper movieDatabaseHelper;

public MovieRepository(LifecycleOwner lifecycleOwner, Context context) {
    this.lifecycleOwner = lifecycleOwner;
    movieApi = getRetrofitHelper().getService(MovieApi.class);
    movieDatabaseHelper = new MovieDatabaseHelper(context);
}

public LiveData<List<Movie>> getMovies() {
    LiveData<List<Movie>> moviesLiveData = movieApi.getMovieList();
    moviesLiveData.observe(lifecycleOwner, new Observer<List<Movie>>() {
        @Override
        public void onChanged(@Nullable List<Movie> movieArrayList) {
            movieDatabaseHelper.Save(movieArrayList);
        }
    });

    return movieDatabaseHelper.getAll();
} }

Activity class

public class HomeActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // the error is here
    HomeViewModel homeViewModel = ViewModelProviders.of(this).get(HomeViewModel.class);

    homeViewModel.getMovies().observe(HomeActivity.this, new Observer<List<Movie>>() {
        @Override
        public void onChanged(@Nullable List<Movie> movieArrayList) {
            String str = null;
            if (movieArrayList != null) {
                str = Arrays.toString(movieArrayList.toArray());
            }
            Log.e("movies", str);
        }
    });
}

}

Should i use Dagger in my project and custom factory?

Answer 1

Quoting the documentation for AndroidViewModel:

Subclasses must have a constructor which accepts Application as the only parameter.

Your constructor does not meet that requirement.

Either:

• Remove the Context context and LifecycleOwner lifecycleOwner constructor parameters from your HomeViewModel, or

• Create a ViewModelProvider.Factory that can build your HomeViewModel instances, and use that factory with ViewModelProviders.of()