Question

I have designed what is essentially a propertychanged listener – i.e. when Instance.A changes, call OnAChanged()

Observable.FromEventPattern<PropertyChangedEventArgs>(Instance,"PropertyChanged")
          .Where(e => e.EventArgs.PropertyName == "A")
          .ObserveOn(Scheduler.ThreadPool)
          .Subscribe(search =>
              OnAChanged((PropertyChangedEventArgsEx)search.EventArgs), s =>
                  OnError(s)); 

This works totally fine (without the s => OnError(s) part).

However, I wanted to test exception handling. I modified by OnAChanged() method to just throw a new exception. However, the exception is thrown, and OnError never gets called, and my application crashes. Am I misunderstanding the usage of OnError?

Answer 1

You are misunderstanding OnError – OnError is a property of the IObservable. Event-based IObservables never OnError (because there’s no such thing as an “Event Exception” or something). If you had a different source, like Observable.Start, you could see the OnError.