Databinding BR not working in my mvvm project in notifyPropertyChanged method

I'm trying to learn mvvm with a simple project but BR not working for me. I import com.example.mvvm.BR to my class but android studio show me cannot resolve symbol BR.

public class UserViewModel extends BaseObservable
{
    private String name;

    private Context context;

    public UserViewModel(User user)
    {
        this.name = name;
    }

    public UserViewModel(Context context)
    {
        this.context = context;
    }

    @Bindable
    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
        notifyPropertyChanged(BR.name);//error 
    }
}

What should I do?