CODEWITHSUNDEEP
c#wcfunity-containerprism
Syed Osama Maruf
Syed Osama Maruf

Reputation: 1935

Prism Event Aggregators and WCF Services and Unity

I am using prism event aggregators to trigger and associate events (publish and subscribe). The service is only instantiated if there is a request for it. Either from a client (through a channel) or from another service (as a class object).

Issue:

Scenario: If I am using lets say WCF services that act as our subscribers and also publishers and the service subsriber instance has not yet been created and the events get triggered,what can be done to handle this since as at this point the subscriber instance has not been created. (Registration has been done though).

Note: I am subscribing to events in the ctor of the service.

So , in short, I am looking to make sure all subscribers are instanstiated before the publish (event trigger call).

Possible Solution: I was looking at Unity application Block to resolve this dependency but wanted to find that if this is the right direction. For this purpose I was thinking of doing something like this in global.asax.cs application start method:

 IUnityContainer container = new UnityContainer();
 container.RegisterType<ISubscribeEvent ,EventSubsriber>();

and then I could 

EventPublisher = container.Resolve<EventPublisher>();

where the ctor of EventPublisher class is

 public EventPublisher(ISubscribeEvent obj)
        {

        }

where ISubscribeEvent will be an interface that every subscriber will implement. So that whenever an event is raised the class implementing ISubscribeEvent interface will be instantiated.

Does this approach make sense? Are there any alternatives?

EDIT:
The events would occur at the server and the subscribers would also be services on the server i.e the service to service call will not be going through the channel but as normal class call.

Update: I have also looked at the IInstanceProvider here as it can provide an interface ,which can be used to control the instantiation of WCF service instances using Unity.WCF.

Upvotes: 0

Views: 414

Answers (1)

Wiktor Zychla
Wiktor Zychla

Reputation: 48240

That won't work.

Event aggregators assume long-living objects, objects that first subscribe to events and then live long enough to get notifications.

WCF service instances are short-living objects. An instance is activated once the request begins and is deleted once the request completed.

The probability that your publisher and subscriber both live in the very same moment of time is low, as you have noticed, the subscriber is not yet created.

I believe your issue stems from the fact that you are misusing event aggregator there. A wcf service can publish events but there is no point in a wcf service being a subscriber registered in an event aggregator. A wcf service already is a subscriber - it can be called by other beings that "notify" it just by calling it.

If you want your services to "notify" other services, just call these other services as you'd normally call them.

Upvotes: 3

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