valider le formulaire avec un bouton de case à cocher RxCocoa/RxSwift

Question

Je dois valider le formulaire avec un bouton radio, mais je n'y arrive pas, je partage mon code :

Mon point de vue :

private func registerForm() {
    tvUserName.rx.text.map { $0 ?? "" }.bind(to: viewModel.userNamePublishSubject).disposed(by: disposeBag)
    tvEmail.rx.text.map { $0 ?? "" }.bind(to: viewModel.emailPublishSubject).disposed(by: disposeBag)
    tvPassword.rx.text.map { $0 ?? "" }.bind(to: viewModel.passwordPublishSubject).disposed(by: disposeBag)
    tvRepeatPassword.rx.text.map { $0 ?? "" }.bind(to: viewModel.repeatPasswordPublishSubject).disposed(by: disposeBag)
    viewModel.formLoginNativaIsValid().bind(to: btnNext.rx.isEnabled).disposed(by: disposeBag)

    checkBoxOutlet.rx.tap
    .scan(false) { lastValue, _ in
        return !lastValue
    }
    .bind(to: btnNext.rx.isEnabled)
    .disposed(by: disposeBag)
}

Mon ViewModel :

let userNamePublishSubject = PublishSubject<String>()
let emailPublishSubject = PublishSubject<String>()
let passwordPublishSubject = PublishSubject<String>()
let repeatPasswordPublishSubject = PublishSubject<String>()

func formLoginNativaIsValid() -> Observable<Bool> {
    return Observable.combineLatest(userNamePublishSubject.asObserver(),
        emailPublishSubject.asObserver(),
        passwordPublishSubject.asObserver(),
        repeatPasswordPublishSubject.asObserver()).map { userName, email, password, repeatPassword in
            return self.validateRegister(userName: userName, email: email, password: password,
                                         repeatPassword: repeatPassword)
    }.startWith(false)
}

private func validateRegister(userName: String, email: String, password: String, repeatPassword: String) -> Bool {
    return userName.count >= 5 && email.isEmail() && password.count >= 5 && repeatPassword.count >= 5 && password == repeatPassword
}

J'ai validé le formulaire, mais j'ai également besoin que l'utilisateur accepte les conditions générales pour que le bouton "Suivant" soit activé.