Viewmodel could not create an instance of the Android Java MVVM class
I’m trying to implement a movie app that allows browsing movies and checking their ratings… When I tried to implement the MVVM model using my MovieListViewModel, I ran into a problem where the debugger told me that I could not create an instance of this class (MovieListViewModel).
What I did was try to follow some tutorials and look for all the questions about the View model in this site, they usually say I should use the constructor of the View model as a public constructor, or in the constructor (parameters and things like that) but I’m sure I followed the guidelines on constructors
(I tried to follow this tutorial to implement the first part of my application)
https://medium.com/@eladb4382/paging-library-viewmodel-livedata-room-and-retrofit-66bf6a0eef9d
I did basically the same code, but I had the error and he didn’t….
This is my ListView model class:
The public class MovieListViewModel extends AndroidViewModel {
private MovieRepository repository;
public MovieListViewModel(@NonNull Application application) {
super(application);
repository = MovieRepository.getInstance(application);
}
public LiveData<PagedList<Movie>> getMovies() {
return repository.getMovies();
}
public LiveData<NetworkState> getNetworkState() {
return repository.getNetworkState();
}}
What’s the problem:
The public class MovieListFragment extension Fragment implements OnMovieItemClicked {
private final String TAG = MovieListFragment.class.getSimpleName() ;
protected MovieListViewModel viewmodel ;
private MovieDetailsViewModel movieDetailsViewModel ;
protected RecyclerView recyclerView ;
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.movie_list_fragment , container , false );
recyclerView = view.findViewById(R.id.moviesRecyclerView);
recyclerView.setLayoutManager(new GridLayoutManager(getContext(),3));
Log.d(TAG , "creating viewmodel ..." );
viewmodel = ViewModelProviders.of(getActivity()).get(MovieListViewModel.class);
observersRegisters() ;
return view;
}
private void observersRegisters() {
final MovieAdapter adapter = new MovieAdapter(this);
viewmodel.getMovies().observe(this , adapter ::submitList);
viewmodel.getNetworkState().observe(this,networkState ->{
adapter.setNetworkState(networkState);
});
recyclerView.setAdapter(adapter);
movieDetailsViewModel = ViewModelProviders.of(getActivity()).get(MovieDetailsViewModel.class);
}
(This is not the whole fragment class, it’s just the part where the error occurs).
The activity I call this fragment is here::
The public class MainActivity extends AppCompatActivity {
private static final String TAG = MainActivity.class.getSimpleName() ;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(findViewById(R.id.fragmentsContainer)!= null) {
if(savedInstanceState != null ){
return ;
}
MovieListFragment listFragment = new MovieListFragment() ;
listFragment.setArguments(getIntent().getExtras());
getSupportFragmentManager().beginTransaction().add(R.id.fragmentsContainer,listFragment).commit();
}}
I also uploaded the entire project to GitHub in case anyone wanted to check this issue :
https://github.com/TheDeathLorD/MovieApp
This is the error I got at runtime :
E/AndroidRuntime: Fatal Exception: main
Process: com.example.movieapp2, PID: 4935
java.lang.RuntimeException: Unable to create an instance of class com.example.movieapp2.ui.viewmodel.MovieListViewModel
In android.arch.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:207)
In android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134)
In android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102)
In com.example.movieapp2.ui.view.MovieListFragment.onCreateView(MovieListFragment.java:40).
Solution
In your case, you
should see the whole log, I tried your code, and there is more information below the error you posted :
Caused by: java.lang.IllegalArgumentException: baseUrl must end in /: http://api.themoviedb.org/3/movie/popular
at retrofit2. Retrofit$Builder.baseUrl(Retrofit.java:515)
at retrofit2. Retrofit$Builder.baseUrl(Retrofit.java:458)
at com.example.movieapp2.repository.network.api.MovieAPIClient.getInstance(MovieAPIClient.java:27)
at com.example.movieapp2.repository.network.paging.NetMoviePageKeyedDataSource.<init>(NetMoviePageKeyedDataSource.java:32)
at com.example.movieapp2.repository.network.paging.NetMovieDataSourceFactory.<init>(NetMovieDataSourceFactory.java:18)
at com.example.movieapp2.repository.MovieRepository.<init>(MovieRepository.java:27)
at com.example.movieapp2.repository.MovieRepository.getInstance(MovieRepository.java:56)
This means that you should add a /
after your baseUrl
Then you’ll see another crash prompt Missing either @GET URL or @Url parameter
. This is because @GET URL is blank in MovieAPIInterface.getMovies
, and I suggest you change baseUrl to http://api.themoviedb.org/3/movie
and pop to @GET annotations