ObservableForProperty(...).Subscribe(_ => Something()) eats exceptions?

[Charles Josephs]

ObservableForProperty(...).Subscribe(_ => Something());

In the code snippet above if the Something() method throws an exception, it is silently eatten.

ObservableForProperty(...).Subscribe(_ => Something(), e => HandleException(e));

Even if I attempt to handle the exception reactively. HandleException is never called. 

I'm relatively new to ReactiveUI and Reactive itself so I may just be missing something obvious. Any ideas?

[Paul Betts]

Hi Charles,

This isn't how Rx works, it makes no guarantees about what happens in the OnNext of the subscribe. If you did something like this:

ObservableForProperty(...).Select(_ => Something().Subscribe(_ => {}, e => HandleException(e));

Then you'd see it show up. Also, ObservableForProperty is mostly deprecated by WhenAny, use that instead :)

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[Charles Josephs]

Ahh I see. I believe I understand why it is the way it is and how your code addresses the situation. My needs were slightly different, however. I needed Something() to be able to throw an exception without breaking the observable -- or to be more accurate, I was in a situation where I was trying use exceptions to control flow. My final solution was to address that design flaw in my code. Thanks, btw, for the heads up with WhenAny :)

[Paul Betts]

The one pattern where breaking the Observable *is* common / useful is in
ReactiveAsyncCommand:

var cmd = new ReactiveAsyncCommand();

cmd.RegisterAsyncObservable(_ => Observable.Throw<int>(new Exception("Oh noes!")))
.ToProperty(this, x => x.SomeInt);

cmd.ThrownExceptions.Subscribe(ex => Console.WriteLine(ex));

Since the thing you pass to RegisterAsyncObservable is a factory method, it
will create a new Observable every time.

--
Paul Betts <pa...@paulbetts.org>

On Wed, May 22, 2013 at 10:04:04AM -0700, Charles Josephs wrote:
> Ahh I see. I believe I understand why it is the way it is and how your code
> addresses the situation. My needs were slightly different, however. I
> needed Something() to be able to throw an exception without breaking the
> observable -- or to be more accurate, I was in a situation where I was
> trying use exceptions to control flow. My final solution was to address
> that design flaw in my code. Thanks, btw, for the heads up with WhenAny :)
>
> On Monday, May 20, 2013 12:00:04 PM UTC-4, Paul Betts wrote:
> >
> > Hi Charles,
> >
> > This isn't how Rx works, it makes no guarantees about what happens in the
> > OnNext of the subscribe. If you did something like this:
> >
> > ObservableForProperty(...).Select(_ => Something().Subscribe(_ => {}, e =>
> > HandleException(e));
> >
> > Then you'd see it show up. Also, ObservableForProperty is mostly
> > deprecated by WhenAny, use that instead :)
> >
> >

> > On Sun, May 19, 2013 at 11:29 AM, Charles Josephs <cjos...@gmail.com<javascript:>

> > > wrote:
> >
> >> ObservableForProperty(...).Subscribe(_ => Something());
> >>
> >>
> >> In the code snippet above if the Something() method throws an exception,
> >> it is silently eatten.
> >>
> >> ObservableForProperty(...).Subscribe(_ => Something(), e =>
> >>> HandleException(e));
> >>
> >>
> >> Even if I attempt to handle the exception reactively. HandleException is
> >> never called.
> >>
> >> I'm relatively new to ReactiveUI and Reactive itself so I may just be
> >> missing something obvious. Any ideas?
> >>
> >> --
> >> You received this message because you are subscribed to the Google Groups
> >> "ReactiveUI mailing list" group.
> >> To unsubscribe from this group and stop receiving emails from it, send an

> >> email to reactivexaml...@googlegroups.com <javascript:>.