CODEWITHSUNDEEP
javaandroidmvvmviewmodel
Digvijay
Digvijay

Reputation: 3281

Unable to create an instance of ViewModel

I have created viewmodel and repository where in constructor I am passing application context as argument in viewmodel and repository class but its showing error and app is crashing.

Below is my stack trace:

2021-02-14 03:24:20.782 8516-8516/com.app.itunes E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.app.itunes, PID: 8516
java.lang.RuntimeException: Cannot create an instance of class com.app.itunes.ViewModels.HistoryViewModel
    at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:221)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
    at com.app.itunes.fragments.HistoryFragment.onCreateView(HistoryFragment.java:38)
    at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2600)
    at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:881)
    at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)

Caused by: java.lang.InstantiationException: java.lang.Class<com.app.itunes.ViewModels.HistoryViewModel> has no zero argument constructor
    at java.lang.Class.newInstance(Native Method)

Below is my code:

HistoryViewModel.java

public class HistoryViewModel extends ViewModel {

 public HistoryRepository historyRepository;
 public LiveData<List<Tracks>> allTracks;

 public HistoryViewModel(Application application){

    historyRepository = new HistoryRepository(application);
 }

 public LiveData<List<Tracks>> allTracks(){
     return historyRepository.myTracks();
  }
}

HistoryRepository.java

public class HistoryRepository {

public TrackDao trackDao;
public LiveData<List<Tracks>> allTracks;
public TrackDb db;

public HistoryRepository(Application application){

    db = TrackDb.getInstance(application);
    trackDao = db.trackDao();
    allTracks = trackDao.getAllTracks();
}

public LiveData<List<Tracks>> myTracks(){

    return allTracks;
 }

}

HistoryFragment.java

private void loadHistory(){

       historyViewModel = new ViewModelProvider(getActivity()).get(HistoryViewModel.class);

       fragmentHistoryBinding.historyRecycler.setHasFixedSize(true);
       fragmentHistoryBinding.historyRecycler.setLayoutManager(new GridLayoutManager(getActivity(),2,GridLayoutManager.VERTICAL, false));

       historyViewModel.allTracks().observe(getActivity(), new Observer<List<Tracks>>() {
           @Override
           public void onChanged(List<Tracks> tracks) {

               if(tracks.size() > 0){
                   HistoryAdapter adapter = new HistoryAdapter();
                   adapter.setTrackList(tracks);
               }
               else{

               }
           }
       });
}

What can I try to resolve this?

Upvotes: 2

Views: 350

Answers (1)

CommonsWare
CommonsWare

Reputation: 1007584

If you need a Jetpack ViewModel that has access to a Context — and if you are not using a dependency inversion system like Dagger/Hilt or Koin — you can use AndroidViewModel. ViewModelProviders and related classes know how to work with both ViewModel and AndroidViewModel "out of the box".

Otherwise, a ViewModel that has a constructor with parameters requires you to create a custom ViewModelProvider.Factory implementation and use that when requesting your viewmodel instance.

Upvotes: 1

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