Re-execute an observable to notify currently subscribed observers

Question

In an Android app scenario, I want to fetch some Observable<Data> from network, and there are multiple Observer<Data> subscribed to it to update corresponding views. In case of error -say a timeout- show a button to the user to try again.

How can I do the try again part? can I tell the observable to re-execute its logic again without re-subscribing to it?

score 2 · Accepted Answer · answered Jan 27 '18 at 19:44

2

Let's assume you have two buttons, "Retry" and "Cancel", initially hidden. Create two Observables retryButtonClicks and cancelButtonClicks. Then, apply the retryWhen operator to the designated download flow and act upon the signals of these button clicks:

download.retryWhen(errors -> {
    return errors
        .observeOn(AndroidSchedulers.mainThread())
        .flatMap(e -> {
            // show the "Retry" and "Cancel" buttons around here
            return Observable.amb(
                    retryButtonClicks.take(1).map(v -> "Retry"),
                    cancelButtonClicks.take(1).map(v -> "Cancel")
                )
                .doOnNext(v -> { /* hide the "Retry" and "Cancel" buttons */ });
    })
    .takeWhile(v -> "Retry".equals(v))
    ;
});

answered Jan 27 '18 at 19:44

akarnokd

69,132
14
157
192

Can you please explain what's happening here? and how to create the buttons observables? – y.allam Jan 29 '18 at 12:00
There is a stream of errors with `retryWhen`. If an error occurs, another flow is mapped in which takes the button click signal from either buttons unless cancel was clicked. Once the "Retry" button was clicked, the `retryWhen` will resubscribe to the source. Please look at the RxBinding library for creating button click `Observable`s. – akarnokd Jan 29 '18 at 12:44
Thanks a lot for the answer and explanation – y.allam Feb 03 '18 at 11:18
Another question, using `retryWhen` prevents the error from being propagated to the observer's `onError` callback. How to solve this while using `retryWhen`? – y.allam Feb 04 '18 at 13:32
What do you mean? – akarnokd Feb 04 '18 at 13:40
Assume observable: `Observable – y.allam Feb 04 '18 at 14:00
In the `flatMap` inside `retryWhen`, check the `e` and return `Observable.error(e)` to stop the retry. – akarnokd Feb 04 '18 at 15:15
But i need to keep both, return the error to be consumed by the Observer, and then execute the retry when retry button clicked! – y.allam Feb 05 '18 at 16:06
That is not possible. The moment the error reaches the Observer, the stream is over. – akarnokd Feb 05 '18 at 17:09

score 1 · Answer 2 · answered Jan 27 '18 at 18:09

1

There is actually specific methods

retry()

Returns an Observable that mirrors the source Observable, resubscribing to it if it calls onError (infinite retry count).

and retry(long count)

Returns an Observable that mirrors the source Observable, resubscribing to it if it calls onError up to a specified number of retries.

Re-execute an observable to notify currently subscribed observers

2 Answers2