Android ViewModel recreated on screen rotation

Question

I found a case when architecture components ViewModel isn\'t retained - in short it goes as follows:

1. Activity is started and ViewModel in

Answer 1

For others that may not be helped by previous answers like me, the problem could be that you haven't set up your ViewModelProvider properly with a factory.

After digging around I solved my similiar problem by adding the following method to my Activities:

protected final  ViewModel obtainViewModel(@NonNull AppCompatActivity activity, @NonNull Class modelClass) {
    ViewModelProvider.AndroidViewModelFactory factory = ViewModelProvider.AndroidViewModelFactory.getInstance(activity.getApplication());
    return new ViewModelProvider(activity, factory).get(modelClass);
}

And then I did this in my Fragments:

protected final  ViewModel obtainFragmentViewModel(@NonNull FragmentActivity fragment, @NonNull Class modelClass) {
    ViewModelProvider.AndroidViewModelFactory factory = ViewModelProvider.AndroidViewModelFactory.getInstance(fragment.getApplication());
    return new ViewModelProvider(fragment, factory).get(modelClass);
}

I already had some abstract super classes for menu purposes so I hid the methods away there so I don't have to repeat it in every activity. That's why they are protected. I believe they could be private if you put them in every activity or fragment that you need them in.

To be as clear as possible I would then call the methods to assign my view model in onCreate() in my activity and it would look something like this

private MyViewModel myViewModel;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    myViewModel = (MyViewModel) obtainViewModel(this, MyViewModel.class);
}

or in fragment

private MyViewModel myViewModel;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getActivity() != null) {
        myViewModel = (MyViewModel) obtainFragmentViewModel(getActivity(), MyViewModel.class);
    }
}

It seems to work fine so far. If someone have a better way please let us know!