RxJava - When and why to use Observable.share()

Question

I\'ve seen patterns like this:

Observable nameChanges = nameDataSource.changes().share();

// One subscriber
autoUnsubscribe(nameChanges.subscribe(         


        

Answer 1

I would not have to think about when I need to share an Observable, and when I don't. I'm afraid that you will have to think when programming. ;)

In the above code, yes, sharing makes sense. But what if you we're updating something on the backend, using the same network and method call from two different points, updating with different data? You would have the same call with the same Observable, but you certainly wouldn't want to share the Observable instance (and the network call) because that means that all successive calls with data would be discarded in the favour of the first one. Or if you wanted to start a timer whenever you're subscribed, you again wouldn't want to share this with other Observables.

Also, it is much easier to add certain behaviour than to remove it. For example, if sharing was the default, and the second subscriber wouldn't want to share and removes the sharing - what about the third one? Will it share it with the first one or not? At that point the sharing property becomes the property of the Subscriber and not the Observable and you would have no clear way of knowing which one is shared and which one isn't.