rxSwift Observable dependency - ios

Question

I’m new to rxSwift. I have 3 observables, the checkAccount, fetchMails and fetchFolders.
fetchMails and fetchFolders depend on the checkAccount result. How can I invoke the fetchMails and fetchFolders operation using the UIButton Tap? And if the checkAccount success, I don't what it to run each time I fetchMails and fetchFolders. If checkAccount Failed, I want to retry checkAccount when fetchMails and fetchFolders. How can I To achieve this purpose? and This is my code:
#IBOutlet weak var btn1: UIButton!
#IBOutlet weak var btn2: UIButton!
var checkAccountO: Observable<Bool>?
let bag = DisposeBag()
let fetchO: Observable<[String]> = Observable.create { observer in
DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(1000)) {
observer.onNext(["1","2"])
}
return Disposables.create()
}
let fetchFolderO: Observable<[String]> = Observable.create { observer in
DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(1000)) {
observer.onNext(["folder1","folder2"])
}
return Disposables.create()
}
override func viewDidLoad() {
super.viewDidLoad()
fetchFolders().subscribe { (evetn) in
print("folders \(evetn)")
}.addDisposableTo(bag)
fetchMails().subscribe { (evetn) in
print("mails \(evetn)")
}.addDisposableTo(bag)
}
func checkAccount() -> Observable<Bool> {
if let ob = checkAccountO {
return ob
}
checkAccountO = Observable.create { (observer) -> Disposable in
print("checking...")
DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(1000)) {
let i = arc4random() % 2
if i == 0 {
print("succ")
observer.onNext(true)
observer.onCompleted()
}else {
print("failed:\(i)")
let err = NSError.init(domain: "err", code: 1001, userInfo: nil)
observer.onError(err)
}
}
return Disposables.create()
}.retry(3).shareReplay(1)
return checkAccountO!
}
func fetchMails() -> Observable<[String]> {
return checkAccount().flatMap({ (_) -> Observable<[String]> in
return self.fetchO
})
}
func fetchFolders() -> Observable<[String]> {
return checkAccount().flatMap({ (_) -> Observable<[String]> in
return self.fetchFolderO
})
}
according to #Timofey Solonin's answer, I change the fetchFoders and fetchMails observable to flatmap from button.rx.tap like this, but still not known how to use retrywhen
func fetchMails() -> Observable<[String]> {
let rxtap = btn1.rx.tap
return rxtap.flatMap { (_) -> Observable<[String]> in
return self.checkAccount().flatMap({ (_) -> Observable<[String]> in
return self.fetchO
})
}
}
func fetchFolders() -> Observable<[String]> {
let rxtap = btn2.rx.tap
return rxtap.flatMap { (_) -> Observable<[String]> in
return self.checkAccount().flatMap({ (_) -> Observable<[String]> in
return self.fetchFolderO
})
}
}

Answer 1

You can use retryWhen operator. flatMap the error stream from retryWhen to checkAccount and if checkAccount will be successful your operation will retry.
To start a stream from button you use button.rx.tap and flatMap it.
For example if you want to fetchMail() from button.rx.tap and checkAcount() multiple times if fetchMail() errored out you can use:
btn1.rx.tap.flatMapLatest {
fetchMails().retryWhen{ errors in
errors.flatMapLatest{ _ in
checkAccount().retry() //or you can use retry(n) if you want to retry checkAccount limited amount of times.
//fetchMails() will repeat if checkAccount() will return anything. Just keep in mind that retryWhen block is not going to be called if checkAccount() was successful.
}
}
}