OnNext not being called on observable when using combineLatest and take

Question

I'm trying to get a subscription to automatically unsubscribe when it emits an item. The base observable is created like this.

public static Observable<RxBleConnection> setupConnection(RxBleDevice device, PublishSubject<Void> disconnectTrigger) {
    return device
            .establishConnection(false)
            .takeUntil(disconnectTrigger)
            .retry(3)
            .retryWhen(o -> o.delay(RETRY_DELAY, TimeUnit.MILLISECONDS))
            .compose(new ConnectionSharingAdapter());
}

Then I try to combine three read operations into a ProgramModel.

private void readCharacteristics(Action1<ProgramModel> onReadSuccess) {
    mConnectionObservable
            .flatMap(rxBleConnection ->
                    // combines the following three observables into a single observable that is
                    // emitted in onNext of the subscribe
                    Observable.combineLatest(
                            rxBleConnection.readCharacteristic(UUID_SERIAL_NUMBER),
                            rxBleConnection.readCharacteristic(UUID_MACHINE_TYPE),
                            rxBleConnection.readCharacteristic(UUID_CHARACTERISTIC),
                            ProgramModel::new))
            .observeOn(AndroidSchedulers.mainThread())
            .take(1)
            .subscribe(programModel -> {
                programModel.trimSerial();
                onReadSuccess.call(programModel);
            }, BleUtil::logError);
}

So theoretically once a program model is comes through oNext of the subscribe, the subscription will be unsubscribed from. For some reason the operation gets stuck and onNext and onError are never called. If I remove the take(1) this works fine but I don't want to have to deal with holding onto a reference to the subscription and unsubscribing manually. Does anyone know what I'm doing wrong or why onNext is not being called?

What is `ConnectionSharingAdapter`. Do the individual `readCharacteristics` produce any items? Put `doOnNext` at various places to see where events disappear. — akarnokd, Dec 07 '17 at 15:09
The connection sharing adapter is part of `RxAndroidBle`. Since every time subscribe is called a connection to the device is created, so the connection sharing adapter basically makes sure only one is active at a time. I'll try the `doOnNext` — David Carek, Dec 07 '17 at 15:12

score 0 · Answer 1 · answered Dec 07 '17 at 15:38

0

I needed to call take(1) before the flatMap as well as after. This post sort of explains it Read multiple characteristics from an Android device using library RxAndroidBle

answered Dec 07 '17 at 15:38

David Carek

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From my knowledge of `RxJava` this should not be the case and the code from original post should work as expected—one of subscribe actions should get called. Could you add `RxBleLog.setLogLevel(RxBleLog.VERBOSE)` and more logging if the part where you create `Observable.combineLatest` is called? There must be some cause of the behaviour you are experiencing. – Dariusz Seweryn Dec 07 '17 at 16:59

OnNext not being called on observable when using combineLatest and take

1 Answers1