BaseActivity.java

public abstract class BaseActivity<T extends ViewModel> extends DaggerAppCompatActivity {

    private T viewModel;

    /**
     *
     * @return view model instance
     */
    public abstract T getViewModel();

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.viewModel = viewModel == null ? getViewModel() : viewModel;
    }

}