RxJava/RxKotlin: Wait for value to be fetched async and then provide to all subscribers

Question

I have a scenario where I have to fetch some string asynchronously. I would like to create a method where I can listen to when this value is fetched successfully and then provided to the listener. Now, this can be done easily via many ways including a callback listener or a lambda.

But what do I use so that all subsequent calls to this method, also provide the string back - without having to fetch it again, as it has already been fetched once. So a solution where the listener is still attached but is provided the value right away since it is available. I know how to do this via old fashioned callback listeners, where the value is stored and then for subsequent calls it can be returned right away via the callback.

But is there a more compact/sophisticated way to do it, let's say via Rx?

Thanks.

score 0 · Answer 1 · answered Aug 23 '20 at 08:20

I think you can just use cache() operator. It will be something like this:

val value: Single<String> by lazy {
    // emulation of your callback
    Single.create<String> { emitter ->
        Thread.sleep(1000)
        println("do some work")
        emitter.onSuccess("test")
    }.cache()
}

fun main() {
    value.subscribe { str -> println(str) }
    value.subscribe { str -> println(str) }
    value.subscribe { str -> println(str) }
    Thread.sleep(2000)
    // output:
    // do some work
    // test
    // test
    // test
}

RxJava/RxKotlin: Wait for value to be fetched async and then provide to all subscribers

1 Answers1