RxJava Zip two observables without completing them

Question

I have two observables: first is from library RxAndroidBle:

Observable<RxBleConnection> bluetoothObservable = RxBleClient.create(getBaseContext()).getBleDevice(macAddress)
.establishConnection(false)

Which connects to device and keeps connection while it has subscribers, and another

Observable<Response> serverObservable = Observable.fromCallable(() -> callServer())

Then I zip them together

bluetoothObservable.zipWith(serverObservable , (rxBleConnection, s) -> {
                                Log.d(TAG, "zip done");
                                return "mock result";
                            }).subscribe((s) -> {},
                                    Throwable::printStackTrace);

But after zip bluetoothObservable gets unsubscribed and connection immediately falls. What should I do to zip those observables and keep bluetoothObservable alive/subscribed?

Dariusz Seweryn · Accepted Answer · 2017-07-05T13:25:32.997

2

Instead of .zip() you can use:

Observable.combineLatest(
  bluetoothObservable, 
  serverObservable,
  (rxBleConnection, s) -> {
    Log.d(TAG, "combined");
    return "mock result";
  }
)
  .subscribe(
    (s) -> {},
    Throwable::printStackTrace
  )

Explanation: zip tries to combine outputs from both Observables one by one. If one of them will complete and all previous emissions from that Observable were matched — there is no point of keeping the subscription to the other Observable as the subsequent emissions will not be used. combineLatest just tries to combine all emissions from both Observables into pairs that are the latest.

edited Jul 05 '17 at 13:25

answered Jul 05 '17 at 12:58

Dariusz Seweryn

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Thanks, I'll give it a try and then report – Nikita Khlebushkin Jul 05 '17 at 13:04
No, I'm afraid `bluetoothObservable` still gets unsubscribed – Nikita Khlebushkin Jul 05 '17 at 13:05
I have just checked the exact same code and it works for me so there are two possible situations: the flow is throwing an exception or your `bluetoothObservable` completes by itself. – Dariusz Seweryn Jul 05 '17 at 13:16
Yes, you're right, an exception is thrown. Thank you for your answer! – Nikita Khlebushkin Jul 05 '17 at 13:21

RxJava Zip two observables without completing them

1 Answers1