When to use Observable.FromEventPattern rather than Observable.FromEvent?

Question

We\'ve got a client calling off to a TIBCO EMS queue and are wiring up the events like this:

var msgConsumer = _session.CreateConsumer(responseQueue);
var re         


        

Answer 1

To elaborate on this a bit further, you can typically determine when to choose one of the FromEvent vs FromEventPattern by the type of event used in the class you're trying to observe. Use FromEventPattern when your event is of type EventHandler or the generic EventHandler. Use FromEvent when you're using a custom, non-generic event handler type. The following examples are lifted directly from the Rx wiki, which has lots of good examples- 101 of them to be exact.

FromEventPattern (with generic EventHandler):

class ObserveEvent_Generic
{
    public class SomeEventArgs : EventArgs { }
    public static event EventHandler GenericEvent;

    static void Main()
    {
        // To consume GenericEvent as an IObservable:
        IObservable> eventAsObservable = Observable.FromEventPattern(
            ev => GenericEvent += ev,
            ev => GenericEvent -= ev );
    }
}

FromEvent:

class ObserveEvent_NonGeneric
{
    public class SomeEventArgs : EventArgs { }
    public delegate void SomeNonGenericEventHandler(object sender, SomeEventArgs e);
    public static event SomeNonGenericEventHandler NonGenericEvent;

    static void Main()
    {
        // To consume NonGenericEvent as an IObservable, first inspect the type of EventArgs used in the second parameter of the delegate.
        // In this case, it is SomeEventArgs.  Then, use as shown below.
        IObservable> eventAsObservable = Observable.FromEvent(
            (EventHandler ev) => new SomeNonGenericEventHandler(ev), 
            ev => NonGenericEvent += ev,
            ev => NonGenericEvent -= ev);
    }
}