RxJava introduced Single<T>. How do I convert an Observable<T> to a Single<T>?

Question

RxJava recently introduced Single. Is there a way to convert an already existing Observable (that's pretty much a Single) to a Single without modifying the source of the original observable?

For example, I have an api service class with a method that returns an Observable - which is essentially fetching a User from a remote resource. Say I can't modify the service. I want to consume this elsewhere but return a Single. How do I do this?

A pinch more background

RxJava recently introduced the concept of a Single which is more or less an Rx friendly simple callback (i.e. an Observable emitting one object or an error) (read more about it here - http://reactivex.io/documentation/single.html)

Answer 1

I think another answer is outdated. You should probably check the following methods.

singleOrError: Emits the one and only element, IndexOutOfBoundsException if the source is longer than 1 item or a NoSuchElementException if the source is empty.

firstOrError: Emits the first element or a NoSuchElementException if the source is empty.

lastOrError: Emits the lastelement or a NoSuchElementException if the source is empty.

elementAtOrError: Emits the indexth element or a NoSuchElementException.

More info on this page: https://github.com/ReactiveX/RxJava/wiki/What%27s-different-in-2.0

Answer 2

Note: This is for RxJava 1. See other answers below/above for Rx2 :)

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2 new convenience methods were added to accomplish this very thing.

toSingle() converts an Observable that emits a single item into a Single that emits that item

toObservable converts a Single into an Observable that emits the item emitted by the Single and then completes

(source: http://reactivex.io/documentation/single.html)

Answer 3

In rxjava2 you can use Single.fromObservable().

Answer 4

https://github.com/apollographql/apollo-android/blob/main/apollo-rx2-support/src/main/java/com/apollographql/apollo/rx2/RxJavaExtensions.kt

There is an extension for ApolloClient.

rxQuery gives you Observable<Response> rxMutate gives you Single<Response>

and see others.