Android ViewModel additional arguments

Question

Is there a way to pass additional argument to my custom AndroidViewModel constructor except Application context. Example:

    public class MyViewModel extends AndroidViewModel {
        private final LiveData<List<MyObject>> myObjectList;
        private AppDatabase appDatabase;

        public MyViewModel(Application application, String param) {
            super(application);
            appDatabase = AppDatabase.getDatabase(this.getApplication());
            
            myObjectList = appDatabase.myOjectModel().getMyObjectByParam(param);
        }
    }

And when I want to user my custom ViewModel class I use this code in my fragment:

    MyViewModel myViewModel = ViewModelProvider.of(this).get(MyViewModel.class)

So I don't know how to pass additional argument String param into my custom ViewModel. I can only pass Application context, but not additional arguments. I would really appreciate any help. Thank you.

Edit: I've added some code. I hope it's better now.

Answer 1

You need to have a factory class for your ViewModel.

public class MyViewModelFactory implements ViewModelProvider.Factory {
    private Application mApplication;
    private String mParam;


    public MyViewModelFactory(Application application, String param) {
        mApplication = application;
        mParam = param;
    }


    @Override
    public <T extends ViewModel> T create(Class<T> modelClass) {
        return (T) new MyViewModel(mApplication, mParam);
    }
}

And when instantiating the view model, you do like this:

MyViewModel myViewModel = new ViewModelProvider(this, new MyViewModelFactory(this.getApplication(), "my awesome param")).get(MyViewModel.class);

For kotlin, you may use delegated property:

val viewModel: MyViewModel by viewModels { MyViewModelFactory(getApplication(), "my awesome param") }

There's also another new option - to implement HasDefaultViewModelProviderFactory and override getDefaultViewModelProviderFactory() with the instantiation of your factory and then you would call ViewModelProvider(this) or by viewModels() without the factory.