RxJava default error handler

Question

Sorry, is there a possibility to set default error handler in RxJava?

For instance, I some code in Utils.kt file:

fun BaseFragment.callGallery(view: View){
    view.clicks().bindToLifecycle(this).subscribe {
        RxPaparazzo.takeImage(this)
        .usingGallery()
        .subscribe { response ->
            throw RuntimeException("Where is this exception from?")
        }
    }
}

But in stacktrace there's no any hint about Utils.kt or about any of my file.

I understand that I can set onError in every subscriber. with code like:

.subscribe ({ response ->
    ....
}, { it.printStackTrace() })

But I'd prefer to set one default onError for all subscribers. How can I do it?

Stacktrace:

05-07 12:11:48.246 10966-10966/ru.egslava.rxfluxtest E/AndroidRuntime: FATAL EXCEPTION: main
 Process: ru.egslava.rxfluxtest, PID: 10966
 java.lang.RuntimeException: Unable to destroy activity {ru.egslava.rxfluxtest/rx_activity_result.HolderActivity}: rx.exceptions.OnErrorNotImplementedException: Where is this exception from?
     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3831)
     at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3849)
     at android.app.ActivityThread.-wrap5(ActivityThread.java)
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1398)
     at android.os.Handler.dispatchMessage(Handler.java:102)
     at android.os.Looper.loop(Looper.java:148)
     at android.app.ActivityThread.main(ActivityThread.java:5417)
     at java.lang.reflect.Method.invoke(Native Method)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
  Caused by: rx.exceptions.OnErrorNotImplementedException: Where is this exception from?
     at rx.internal.util.InternalObservableUtils$ErrorNotImplementedAction.call(InternalObservableUtils.java:374)
     at rx.internal.util.InternalObservableUtils$ErrorNotImplementedAction.call(InternalObservableUtils.java:371)
     at rx.internal.util.ActionSubscriber.onError(ActionSubscriber.java:44)
     at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157)
     at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120)
     at rx.exceptions.Exceptions.throwOrReport(Exceptions.java:204)
     at rx.observers.SafeSubscriber.onNext(SafeSubscriber.java:144)
     at rx.internal.operators.OperatorOnErrorResumeNextViaFunction$4.onNext(OperatorOnErrorResumeNextViaFunction.java:153)
     at rx.internal.operators.OperatorMap$MapSubscriber.onNext(OperatorMap.java:74)
     at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:391)
     at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:353)
     at rx.internal.operators.OperatorMerge$InnerSubscriber.onNext(OperatorMerge.java:838)
     at rx.observers.Subscribers$5.onNext(Subscribers.java:229)
     at rx.internal.operators.OperatorZip$Zip.tick(OperatorZip.java:264)
     at rx.internal.operators.OperatorZip$Zip$InnerSubscriber.onNext(OperatorZip.java:335)
     at rx.internal.operators.OperatorMap$MapSubscriber.onNext(OperatorMap.java:74)
     at rx.internal.util.ScalarSynchronousObservable$WeakSingleProducer.request(ScalarSynchronousObservable.java:268)
     at rx.Subscriber.setProducer(Subscriber.java:211)
     at rx.internal.operators.OperatorMap$MapSubscriber.setProducer(OperatorMap.java:99)
     at rx.internal.util.ScalarSynchronousObservable$1.call(ScalarSynchronousObservable.java:79)
     at rx.internal.util.ScalarSynchronousObservable$1.call(ScalarSynchronousObservable.java:75)
     at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:50)
     at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
     at rx.Observable.unsafeSubscribe(Observable.java:8452)
     at rx.internal.operators.OperatorZip$Zip.start(OperatorZip.java:214)
     at rx.internal.operators.OperatorZip$ZipSubscriber.onNext(OperatorZip.java:156)
     at rx.internal.operators.OperatorZip$ZipSubscriber.onNext(OperatorZip.java:122)
     at rx.internal.util.ScalarSynchronousObservable$WeakSingleProducer.request(ScalarSynchronousObservable.java:268)
     at rx.Subscriber.setProducer(Subscriber.java:209)
     at rx.internal.util.ScalarSynchronousObservable$1.call(ScalarSynchronousObservable.java:79)
     at rx.internal.util.ScalarSynchronousObservable$1.call(ScalarSynchronousObservable.java:75)
     at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:50)
     at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
     at rx.Observable.unsafeSubscribe(Observable.java:8452)
     at rx.internal.util.ScalarSynchronousObservable$4.call(ScalarSynchronousObservable.java:227)
     at rx.internal.util.ScalarSynchronousObservable$4.call(ScalarSynchronousObservable.java:220)
     at rx.Observable.unsafeSubscribe(Observable.java:8452)
     at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:248)

Answer 1

RxJava has Plugins to support cross cutting concerns nicely. In particular RxJavaErrorHandler is desiged to attached global error handling behavior like so:

RxJavaPlugins.getInstance().registerErrorHandler(object : RxJavaErrorHandler() {
    override fun handleError(e: Throwable?) {
        println("Global error handler: $e")
    }
})

Observable.just(1).concatMap({ Observable.error<Int>(Exception("Just throwing $it")) })
        .subscribe({
            println("I'll not be called")
        }, {
            println("Specific error handler: $it")
        })

The above code would print:

Error occurred java.lang.Exception: Just throwing 1
A default error handler: java.lang.Exception: Just throwing 1

I suspect that you'd also be interested in improving diagnostic information available in stacktraces when you do have an unhandled error. For that there's a RxJavaStackTracer that when used RxJavaPlugins.getInstance().registerObservableExecutionHook(RxJavaStackTracer()) enhaces stack trace information. The Stacktraces and subscribeOn/observeOn issue on github is a good read on the topic.