Why RxJava with Retrofit on Android doOnError() does not work but Subscriber onError does

Question

can someone explain me why code like this:

 networApi.getList()
            .subscribeOn(Schedulers.newThread())
            .observeOn(AndroidSchedulers.mainThread())
            .doOnError(throwable -> {
                throwable.getMessage();
            })
            .doOnNext(list -> {
                coursesView.populateRecyclerView(list);
                courseList = (List<Course>) courses;
            }).subscribe();

If there is no internet goes into doOnError but throws it further so the app goes down, but code like this:

networkApi.getList()
            .subscribeOn(Schedulers.newThread())
            .observeOn(AndroidSchedulers.mainThread())
            .subscribe(new Subscriber<List<? extends Course>>() {
                @Override
                public void onCompleted() {

                }

                @Override
                public void onError(Throwable e) {
                    e.getMessage();
                }

                @Override
                public void onNext(List<? extends Course> list) {
                    coursesView.populateRecyclerView(list);
                    courseList = (List<Course>) list;
                }
            });

Work how I expect, it means when there is no internet connection it does nothing.

Answer 1

Basically, doOnError does not handle the error, in the sense that it does not consume it. It just does something with it, log it, for example. (The same is true for doOnNext - it also does not consume the item and the item still ends up in onNext of the Subscriber).

The error is still sent down the chain and would still end up in the onError of your Subscriber.

I am pretty certain that your app is crashing with an OnErrorNotImplementedException and that is because you don't have any Subscriber at all and therefore no onError method.