How to show/hide the progressHUD, with MVVM and RxSwift in swift

I'm beginning with MVVM in order to well separate logic code from the view. But I have some concern about where to put the progressHUD related code when tapping a button that makes a request.

Before, I used to do that:

//Before 
@IBAction func startRequestTapped() {
   SVProgressHUD.show()
    self.apiClient.requestObservable().subscribe(onError: { (error) in
        SVProgressHUD.hide()                    
    }, onCompleted: { 
        SVProgressHUD.hide()                                        
    })
}

But when I use mvvm, I do like that:

//In the viewModel
public var validateButtonDidTap = PublishSubject<Void>()
init() {
    validateButtonDidTap.flatMap { (_)
        return self.apiClient.requestObservable()
    }
}


   // In the viewController
viewDidLoad() {
    let tap = self.validateButton.rx.tap
    tap.bindTo(self.viewModel.validateButtonDidTap)
}

And amongst that, I don't know where to put the the ProgressHUD hide or show.

Mark answer is right, but I am going to guide you step by step.

Let's supose you're going to try signing in.

1. Copy ActivityIndicator.swift file in your project.

2. In the viewModel:

   //MARK: - Properties
   
   /// The http client
   private let apiClient: YourApiClient
   
   /// Clousure when button is tapped
   var didTappedButton: () -> Void = {}
   
   /// The user 
   var user: Observable<User>
   
   /// Is signing process in progress
   let signingIn: Observable<Bool> = ActivityIndicator().asObservable()
   
   //MARK: - Initialization
   
   init(client: YourApiClient) {
       self.client = client
   
       self.didTappedButton = { [weak self] in
           self.user = self.apiClient
                           .yourSignInRequest()
                           .trackActivity(self.signingIn)
                           .observeOn(MainScheduler.instance)
       }
   }
   

3. Create an extension of SVProgressHUD: (I don't know SVProgressHUD library, but it would be something like this. Please fix it if needed)

   extension Reactive where Base: SVProgressHUD {
   
       /// Bindable sink for `show()`, `hide()` methods.
       public static var isAnimating: UIBindingObserver<Base, Bool> {
           return UIBindingObserver(UIElement: self.base) { progressHUD, isVisible in
               if isVisible {
                   progressHUD.show() // or other show methods
               } else {
                   progressHUD.dismiss() // or other hide methods
               }
           }
       }
   
   }
   

4. In your viewController:

   @IBAction func startRequestTapped() {
       viewModel.didTappedButton()
   }
   
   override func viewDidLoad() {
   
       // ...
   
       viewModel.signingIn
                .bindTo(SVProgressHUD.rx.isAnimating)
                .addDisposableTo(disposeBag)
   }