AsObservable() extension method for Prism's event aggregator

CompositePresentationEventExtensions.cs

using System;
using Microsoft.Practices.Prism.Events;

// ReSharper disable CheckNamespace
namespace Microsoft.Practices.Prism.Events
// ReSharper restore CheckNamespace
{
    public static class CompositePresentationEventExtensions
    {
        public static IObservable<TEventArgs> AsObservable<TEventArgs>(this CompositePresentationEvent<TEventArgs> @event)
        {
            return new CompositePresentationEventObservable<TEventArgs>(@event);
        }
    }

    public class CompositePresentationEventObservable<TEventArgs> : IObservable<TEventArgs>
    {
        private readonly CompositePresentationEvent<TEventArgs> @event;

        public CompositePresentationEventObservable(CompositePresentationEvent<TEventArgs> @event)
        {
            if (@event == null) throw new ArgumentNullException("event");
            this.@event = @event;
        }

        public IDisposable Subscribe(IObserver<TEventArgs> observer)
        {
            return new CompositePresentationEventSubscription<TEventArgs>(@event, observer);
        }
    }

    public class CompositePresentationEventSubscription<TEventArgs> : IDisposable
    {
        private readonly IObserver<TEventArgs> observer;
        private readonly CompositePresentationEvent<TEventArgs> @event;

        public CompositePresentationEventSubscription(CompositePresentationEvent<TEventArgs> @event, IObserver<TEventArgs> observer)
        {
            if (@event == null) throw new ArgumentNullException("event");
            if (observer == null) throw new ArgumentNullException("observer");

            this.@event = @event;
            this.observer = observer;

            @event.Subscribe(observer.OnNext, true);
        }

        protected virtual void Dispose(bool disposing)
        {
            if (disposing)
            {
                @event.Unsubscribe(observer.OnNext);
            }
        }

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        ~CompositePresentationEventSubscription()
        {
            Dispose(false);
        }
    }
}