How to handle exceptions in OnNext when using ObserveOn?

Question

My application terminates when an error is thrown in OnNext by an observer when I use ObserveOn(Scheduler.ThreadPool). The only way I have found to

Answer 1

You're right - it should feel bad. Using and returning subjects like this is not a good way to go.

At the very least you should implement this method like so:

public static IObservable ExceptionToError(this IObservable source)
{
    return Observable.Create(o =>
    {
        var subscription = (IDisposable)null;
        subscription = source.Subscribe(x =>
        {
            try
            {
                o.OnNext(x);
            }
            catch (Exception ex)
            {
                o.OnError(ex);
                subscription.Dispose();
            }
        }, e => o.OnError(e), () => o.OnCompleted());
        return subscription;
    });
}

Notice there are no subjects used and that if I catch an error that I then dispose of the subscription to prevent the sequence continuing past an error.

However, why not just add an OnError handler in your subscription. A bit like this:

var xs = new Subject();

xs.ObserveOn(Scheduler.ThreadPool).Subscribe(x =>
{
    Console.WriteLine(x);
    if (x % 5 == 0)
    {
        throw new System.Exception("Bang!");
    }
}, ex => Console.WriteLine(ex.Message));

xs.OnNext(1);
xs.OnNext(2);
xs.OnNext(3);
xs.OnNext(4);
xs.OnNext(5);

This code catches the error properly in the subscription.

The other method is to use the Materialize extension method, but that may be a little overkill unless the above solutions don't work.