rxjava2 best practice to create an Observable from an existing Callback function

Question

I am new to rxjava2, and I want to use it to work with my existing code to solve the ignoring Callback hell. The main task is something like the code below :

SomeTask.execute(new Callback() {
    @Override
    public void onSuccess(Data data) {
        // I want to add data into observable stream here
    }
    @Override
    public void onFailure(String errorMessage) {
        // I want to perform some different operations 
        // to errorMessage rather than the data in `onSuccess` callback.
        // I am not sure if I should split the data stream into two different Observable streams 
        // and use different Observers to accomplish different logic.
        // and I don't know how to do it.
    }
}

I have done some digging in Google and Stackoverflow, but still didn't find the perfect solution to create a observable to achieve these two goals.

Wrap a existing Callback function.
Process different Callback data in different logic.

Any suggestion would be a great help.

@akarnokd emitter.onError() can only pass an exception to observer, I am not sure how to pass a customized ErrorMessage object to observer. Any ideas? — Raymond Zhao
– Raymond Zhao, Commented Oct 12, 2017 at 12:39
Use Pair<Data, ErrorMessage> as the type so you can have multiple of the two. — akarnokd
– akarnokd, Commented Oct 12, 2017 at 12:40
@akarnokd emmm.. not a very "pretty" way as I expected. I was wondering if there is a "split" operator or somehing like that. Thanks anyway, I will have it try. — Raymond Zhao
– Raymond Zhao, Commented Oct 12, 2017 at 12:45
One more thing you should look at is setting a disposable/cancellable on your emitter. In case a subscription gets disposed before you complete emitting, it will be important for you to dump resources and stop your execution of "producer". — Dhruv Jagetiya
– Dhruv Jagetiya, Commented Oct 12, 2017 at 14:40

Ulisses Curti · Accepted Answer · 2018-09-11 18:00:09Z

3

Take a look at this article. It will help you.

Here is an possible solution to your problem (Kotlin):

Observable.create<Data> { emitter ->
        SomeTask.execute(object: Callback() {

            override void onSuccess(data: Data) {
                emitter.onNext(data)
                emitter.onComplete()
            }

            override void onFailure(errorMessage: String) {
                // Here you must pass the Exception, not the message
                emitter.onError(exception)
            }
        }
}

Do not forget to subscribe and dispose the Observable.

You must also consider using Single, Maybe or any of the other Observable types.

edited Sep 11, 2018 at 18:00

answered Mar 16, 2018 at 14:26

Ulisses Curti

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