Rx - unsubscribing from events

Question

I have an INotifyPropertyChanged object, Foo. I turn Foo into an observable stream of events using Rx's FromEvent method:

var myFoo = new Foo();
var eventStream = Observable.FromEvent<PropertyChangedEventArgs>(myFoo, "PropertyChanged");

Now I want to listen for a particular property changed, and if .Progress == 100, unsubscribe:

eventStream
   .Where(e => myFoo.Progress == 100)
   .Subscribe(OnFooFinished);

How can I unsubscribe when Progress == 100? If I add a .Take(1) call after the .Where clause, would that automatically unsubscribe?

Answer 1

One option is to use return value of Subscribe:

IDisposable subscription = eventStream.Where(e => myFoo.Progress == 100)
                                      .Subscribe(OnFooFinished);

...

// Unsubscribe
subscription.Dispose();

I suspect that using Take(1) would indeed unsubscribe though, and it may be neater for you. Having looked at it a bit, I'm pretty sure this would unsubscribe, as it'll fire the "completed" message, which generally unsubscribes automatically. I don't have time to check this for sure at the moment, I'm afraid :(

Answer 2

You could use the TakeWhile method:

eventStream.TakeWhile(e => myFoo.Progress != 100);

TakeWhile will dispose the underlying observable sequence when its predicate returns false, you will not have to call dispose manually.