Rx `retryPromptOn` operator. Prompt a user to retry a sequence if an error is emitted

RxRetryPromptOn.swift

extension ObservableType {
    public func retryPromptOn(_ vc: UIViewController) -> Observable<E> {
        return self.retryWhen { (error: Observable<Error>) -> Observable<Void> in
            return vc.rx.retryPrompt(error: error)
        }
    }
}
extension Reactive where Base: UIViewController {
    func retryPrompt(error: Observable<Error>) -> Observable<Void> {
        let retry =  PublishSubject<Void>()
        error.subscribe { (error: Event<Error>) in
            let alert = UIAlertController(title: error.element?.localizedDescription, message: "Retry?", preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "No", style: .cancel) { _ in
                retry.onError(error.element!)
            })
            alert.addAction(UIAlertAction(title: "Retry", style: .default) { _ in
                retry.onNext()
            })
            self.base.present(alert, animated: true)
        }
        return retry
    }
}

Usage (assuming your are on a view controller)

let error = NSError(domain: "...", code: 1, userInfo: [NSLocalizedDescriptionKey: "Didn't work..."])
let observable = Observable<Int>.create { (observer) -> Disposable in
    observer.onNext(1)
    observer.onNext(2)
    observer.onError(error)
    return Disposables.create()
}
observable.retryPromptOn(self).subscribe { print($0) }