Beginning RxSwift - Part 7: Challenge: | Ray Wenderlich Videos

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1

Get introduced to the do operator for performing side effects, and then use the do operator in an example from the previous video.

This is a companion discussion topic for the original entry at https://www.raywenderlich.com/4743-beginning-rxswift/lessons/7
3

What is difference between following:
Case 1:

let observable = Observable<Any>.never()
  observable
    .do(onNext: { (test) in
      print(test)
    }, onError: { (error) in
      print("Error")
    }, onCompleted: {
      print("Completed do")
    }, onSubscribe: {
      print("Subscribe do")
    }, onSubscribed: {
      print("Subscribed do")
    }, onDispose: {
      print("Dispose do")
    })
  observable
    .subscribe(
      onNext: { element in
        print(element)
    },
      onCompleted: {
        print("Completed")
    },
      onDisposed: {
        print("Disposed")
    }
  )

Case 2:

let observable = Observable<Any>.never()
observable
    .do(onNext: { (test) in
      print(test)
    }, onError: { (error) in
      print("Error")
    }, onCompleted: {
      print("Completed do")
    }, onSubscribe: {
      print("Subscribe do")
    }, onSubscribed: {
      print("Subscribed do")
    }, onDispose: {
      print("Dispose do")
    })
    .subscribe(
      onNext: { element in
        print(element)
    },
      onCompleted: {
        print("Completed")
    },
      onDisposed: {
        print("Disposed")
    }
  )

In the above mentioned case, 1st snippet doesn’t print the statements of ‘do’ operator while 2nd case works as expected. What is the difference?

4

In the first snippet do is not part of a subscription.

5

Ok, so do works only when it is part of chained subscription call?

6

@scotteg Can you please help with this when you get a chance? Thank you - much appreciated! :]

7

Correct. An observable emits to subscribers. do is a side effect, not a subscription.

8

Thank you. More clearer now

9

not clear to me why on console prints only once “about to subscribe” with my test shouldn’t I see “disposed in do” too?:

let disposeBag = DisposeBag()
let neverObservable = Observable<Any>.never()

neverObservable

    .do(
        onSubscribe: {
            print("about to subscribe")
    },
        onDispose: {
            print(print("disposed in do"))
    })

    .subscribe(
        onNext: { element in
        print(element)
    },
        onCompleted: {
        print("OK! Completed!")
    },
       onDisposed: {
        print("disposed")
    })
    .disposed(by: disposeBag)