Rx Java: Sleep before OnNext (Sleep before emitting from Observable)

Question

Basis a condition in my Observable, I want to delay onNext / onError. My code is as follows:

 fun check3(){
        val list = arrayListOf(1,2,3,4,5,6,7, null)
        val obs = Observable.create<Int> { subscriber ->
           list.filter {
                it != null
            }.map {
                if (it!! %2 == 0 ) {
                    Thread.sleep(3000)
                    subscriber.onError(IllegalArgumentException("Mod is true"))
                } else {
                    subscriber.onNext(it)
                    subscriber.onComplete()
                }
            }
        }
    }

A sore here being Thread.sleep(3000)

Is there a better way of doing this? Basically I want to delay the onError notification to my subscriber if the if(it %2) condition is met

Answer 1

You can use concatMap to turn the sleep into a non-blocking delay:

Observable.fromIterable(list.filter { it != null })
.concatMap {
    if (it!! % 2 == 0) {
        return@concatMap Observable.error(IllegalArgumentException("Mod is true"))
                         .delay(3, TimeUnit.SECONDS, true)
    }
    Observable.just(it)
}
.take(1)