【Android】Analysis of Empty Observable in RxJava

About Empty Observable

In rxjava, there is a function called Observable.empty()

This function return an object that is instance of ObservableEmpty

This class will emit a complete event instead of next event, then rx chain will ended

Empty Observable with Map Operator

Now let’s test what will happen, when ObservableEmpty is not top level observables

I means it was mapped from other observables by operator such as flatMap

Trial Code

Observable.just(1, 2, 3, 4, 5, 6, 7, 8, 9)
    .flatMap {
        if (it != 5) {
            return@flatMap Observable.just(it.toString())
        }
        return@flatMap Observable.empty<String>()
    }
    .doOnNext { println(it) }
    .subscribe()

We get this result

1
2
3
4
6
7
8
9

When it’s a mediator observable, it won’t interrupt all top observables

It just break the sub event stream that related to itself

Empty Observable with ConcatArray Operator

This time, we make it the top ones, but not the single one

We combine it with other normal observables by concatArray , as top level observable in total

Observable.concatArray(
    Observable.just(1),
    Observable.just(2),
    Observable.just(3),
    Observable.empty(),
    Observable.just(4),
    Observable.just(5)
).flatMap {
    if (it != 5) {
        return@flatMap Observable.just(it.toString())
    }
    return@flatMap Observable.empty<String>()
}
    .doOnNext { println(it) }
    .subscribe()

This is the output

1
2
3
4

We can see that, ObservableEmpty interrupt other observables in the same level

Also, it interrupt the whole rx chain, directlly jump to onComplete

Summary

• ObservableEmpty will interrupt datas or observables mapped from it

• ObservableEmpty will interrupt observables at same level, but after it in order

Bless

Lesson is Over, Have A Rest, and Enjoy Your Life .

Good Work, Good Study, Good Progress, and Good Mood !