Sequence of actions with RxSwift

Question

I'm using RxSwift to simply my code. For my current project I'd like to apply RxSwift's principles to a mess of completion blocks from the LayerKit:

layerClient.connectWithCompletion { (success, error) -> () in
  if (!success) {
     // Error     
  } else {
    layerClient.requestAuthenticationNonceWithCompletion { (nonce, error) -> () in
      // Even more blocks
    }
  }
}

I'm thinking about something like this:

// In extension
public func rx_connect() -> Observable<Bool> {
    return create { observer in

        self.connectWithCompletion { (success, error) -> ()in
            if (success) {
                observer.on(.Next(success))
                observer.on(.Completed)
            } else {
                observer.on(.Error(error))
            }
        }
        return NopDisposable.instance
    }
} 

public func rx_requestAuthenticationNonce() -> Observable<String> {
    // Same for annother method
}

// In AppDelegate
self.layerClient.rx_connect()
 .then() // requestAuthenticationNonceWithCompletion and use the nonce for next action
 .then()
 .subscribeNext(…
 .onError(… // To catch all errors

RxSwift does not have a then() method. Is there another way to do this chaining stuff or am I thinking wrong on how to use ReactiveX in general?

Answer 1

Right, RxSwift doesn't have the then operator because the name is very risky.

then can be a lot of things in the Reactive Extensions world a map a flatMap or even a switchLatest, depending on the context.

In this case I would suggest to use a flatMap because that is going to be returned using a map is an Observable of Observables, that in most cases are hard to combine and manage. So I would do:

self.layerClient.rx_connect()
 .flatMap(){ _ in
   return rx_requestAuthenticationNonce()
             .catchError(displayError)
 }
 .subscribeNext(…
 .onError(… // To catch all errors

I would use flatMap instead of map in this case because I am then able to catch errors without terminating the sequence in case rx_requestAuthenticationNonce() fails.

Be careful in using the catchError operator, this operator will terminate the sequence after recovering and any extra event will be ignored after that.