问题
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)
回答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I think another answer is outdated.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
回答2:
Note: This is for RxJava 1. See other answers below/above for Rx2 :)
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)
回答3:
In rxjava2 you can use Single.fromObservable().
来源：https://stackoverflow.com/questions/36627927/rxjava-introduced-singlet-how-do-i-convert-an-observablet-to-a-singlet