Rx Timeout Operator

Question

I want to emmit one item after x seconds if no items have been emited. I was trying to use the timeout operator. The problem is that timeout operator requires at least one item to be executed previously to start the countdown. From the documentation:

"If the next item isn't emitted within the specified timeout duration starting from its predecessor, the resulting Observable begins instead to mirror a fallback Observable."

That is not the behaviour I'm looking for. When I subscribe to my observable, I want to emit a particular item if a particular period of time elapses without any emitted items previously.

Example:

 getUserLocationFromGPS() //Sometimes I dont receive user location
.timeout(5, TimeUnit.SECONDS, Observable.just(getDefaultLocation())
.subscribe(...);

@KrzysztofSkowronek I don't want to emit the default location at first, it is only the fallback case. — Victor Manuel Pineda Murcia
– Victor Manuel Pineda Murcia, Commented Oct 3, 2017 at 10:23

Benjamin · Accepted Answer · 2017-10-03 10:00:40Z

4

final Observable data = yourApi.getData().take(5, TimeUnit.SECONDS);
final Observable fallback = Observable.just("Fallback");

Observable.concat(data, fallback).firstOrError()
            .subscribe(
                    System.out::println
            );

If yourApi.getData() does not emit anything then you will receive data from your fallback observable.
If yourApi.getData() timeouts then you will receive data from your fallback observable.
If yourApi.getData() emits normally then you will receive data from it.

edited Oct 3, 2017 at 10:00

answered Oct 3, 2017 at 9:20

Benjamin

7,4686 gold badges44 silver badges66 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Victor Manuel Pineda Murcia Over a year ago

Hi, I am already using that parameter. Mi problem is not that. You are always emitting one item, "Hello". In my case, I could have no items emitted previously, so the timeout operator does not start the countdown.

Benjamin Over a year ago

@VictorManuelPinedaMurcia Can you mark the answer as accepted for clarity purpose then? Glad to help!

Krzysztof Skowronek · Accepted Answer · 2017-10-03 10:30:54Z

0

I don't use java-rx specifically, but here is an idea:

getUserLocationFromGPS()
.buffer(5 sec, 1 item) //not sure how to do this in rx-java
.map(x => { // this is select in .net
    if(x.IsEmpty)
      return getDefautLocation();
    else
      return x[0];
    }).Subscribe(...)

buffer will get you list of items every 5sec. You can specify it to return after only 1 item was emited by getUserLocationFromGPS()

map will check if the list is empty (no item was emited) and return proper value

answered Oct 3, 2017 at 10:30

Krzysztof Skowronek

2,9661 gold badge17 silver badges37 bronze badges

1 Comment

Victor Manuel Pineda Murcia Over a year ago

I'm afraid it not working for me. If getUserLocationFromGPS() doesn't emit an item, buffer not emit a empty list after 5 secs. Map operator it not executed in that case. I will stick to Benjamin solution. Thanks you very much!

Collectives™ on Stack Overflow

Rx Timeout Operator

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related