Kotlin type mismatch when using RxJava retryWhen operator - kotlin

Question

I am trying create Observable, which will retryWhen when the network connection will be established.
I've created subject:
private val retrySubject = PublishSubject.create<Unit>()()
And I am using it like this:
private fun publishNetworkReconnection() {
compositeDisposable?.add(
connectionHelper.observeConnection()
.subscribe {connected: Boolean
if(connected){
retrySubject.onNext(null)
}
}
)
}
Then I am trying to use it in my retryWhen operator:
val disposable =
Flowable.interval(0, UPDATE_INTERVAL, TimeUnit.SECONDS, Schedulers.io())
.onBackpressureDrop()
.flatMapCompletable {
revocationRepository.sync(event.id)
}
.retryWhen { retryHandler -> retryHandler.flatMap({ nothing -> retrySubject.asObservable() }) }
.observeOn(AndroidSchedulers.mainThread())
.subscribe({ }, { Timber.e(it, "Unable to sync blacklist") })
compositeDisposable?.add(disposable)
}
How to use it properly in this case?
I am getting this error in Android Studio:
Type mismatch. Required: Publisher<< out (???..???) >>! Found: Observable<
Void
!>!

Answer 1

The problem is, you are mixing RxJava 1 - Subject.asObservable and RxJava 2 - Flowable.
The signature of retryWhen from RxJava 2 is:
Flowable<T> retryWhen(Function<? super Flowable<Throwable>,? extends Publisher<?>> handler)
so lambda inside retryWhen should return something that extends Publisher. Instead, you are returning Subject<Unit> which is converted to Observable<Void>, because apparently your Subject is from RxJava 1. And - because of RxJava version difference - obviously it doesn't extend Publisher.
So error message is correct, retryWhen expects Publisher from RxJava 2, but you give Obervable from RxJava 1. You didn't notice different packages, because they are not included in message.
The main issue is mixing code from RxJava 1 and RxJava 2 which is never good.