RxSwift How to subscribe a observable only one time?

Question

I want to subscribe to an observable, but in some logic, I will re-subscribe to it. If I don't want to write some special logic for it, how can I dispose the last subscription when I add a new one? Or, when I subscribe to it, how can I know if this observable has been subscribed to already?

Solution 1

The simplest solution for what you are looking for is indeed the method that they provided for just that - func take(_ count: Int).

Here is a playground sample:

import RxSwift

var variable = Variable(1)
variable.asObservable().take(1).subscribe(
    onNext: { print("onNext: \($0)") },
    onError: { print("onError: \($0)") },
    onCompleted: { print("onCompleted") },
    onDisposed: { print("onDisposed") })
variable.value = 2

print("done")

The results are:

onNext: 1
onCompleted
onDisposed
done

And yes, this is useful in places where you want to filter an event through a stream, in a location where it is awkward to store a subscription.

Solution 2

Why do you want to do that? What problem are you specifically trying to solve?

The usual way to dispose subscriptions is to use a dispose bag.

func subscribeMyObservable()
{
    disposeBag = DisposeBag()

    myObservable
       .subscribe(onNext: { print("Whatever") }
       .addDisposableTo(disposeBag)
}

Notice how I recreate the disposable every time before subscribing? That would get rid of the previous subscriptions.