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Listening to a single value from an Rx observable sequence

I have an observable sequence and I want to observe only a defined number of values, the number is immaterial, the important part is the fact I don't want to be notified of any further values.

How can this can be achieved?

The answer is easy, use the Rx extension method Take, it'll return the required number of values only. A simple example:

   1:  Observable.FromEventPattern<RoutedEventArgs>(clickButton, "Click")
   2:      .Take(1)
   3:      .ObserveOn(Scheduler.CurrentThread)
   4:      .Subscribe(vt => Debug.WriteLine("{0}: Click called...", ++count));

When the button is clicked in the UI it produces a line in the output window in visual studio:
So using the Take method I can limit the number of observations irrespective of the number of times I click the 'Click Me!' button:

   1:  Observable.FromEventPattern<RoutedEventArgs>(clickButton, "Click")
   2:      .Take(1)
   3:      .ObserveOn(Scheduler.CurrentThread)
   4:      .Subscribe(vt => Debug.WriteLine("{0}: Click called...", ++count));
I was then wondering, and this is the reason for the post:

What's happened to the under lying subscription, has it been disposed?

The seems very similar to a previous post about Rx subscribers and what happens to subscriptions when the OnCompleted is invoked by the disposing the under lying stream. I suspect the answer is 'I don't have anything to worry about, it will all be disposed automatically'.

Lets find out by assigning the subscription to a variable and when the form is closed check the internals of the subscription - yes I am mixing metaphors for .Net event handling ;)
Okay, wasn't expecting that! The under lying composite disposable hasn't been disposed as I was expecting...

I was really expecting it to be automatically disposed at this point, I wonder if adding an OnCompleted implementation for the subscription makes any difference:
So now the subscription is being disposed automatically...

WTF! - How does defining an OnCompleted method mean it can be disposed? Surely what defines it as being eligible for disposing is we're using the Take method with a value of 1.

Now you could say:

'Why worry, I'm sure Rx will take care of it...'

I say anything I create\instantiate which is disposable I am responsible for make sure it is cleaned-up, and this is especially important if you have transient scopes which are regularly being created and destroyed.

Also, the fact I'm using the FromEventPattern extension is not important, the behaviour of the Take method is.

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