Programming WCF Services, 3rd Edition

The Publish-Subscribe Framework

ServiceModelEx contains a simple-to-use, industrial-strength publish-subscribe framework. I wanted to provide not just a publish-subscribe service, but also a general-purpose framework that automates implementing such services and adding the support for any application in just one line of code (if that). The first step in building the framework was to factor the publish-subscribe management interfaces and provide separate contracts for transient and persistent subscriptions and for publishing.^[9]

Managing Transient Subscriptions

For managing transient subscriptions, I defined the ISubscriptionService interface shown in Example D-1.

Example D-1. The ISubscriptionService interface manages transient subscribers

[ServiceContract]
public interface ISubscriptionService
{
   [OperationContract]
   void Subscribe(string eventOperation);

   [OperationContract]
   void Unsubscribe(string eventOperation);
}

Note that ISubscriptionService does not identify the callback contract its implementing endpoint expects. Being a general-purpose interface, it is unaware of particular callback contracts. It is up to the using application to define those callback contracts. The callback interface is provided in the using application by deriving from ISubscriptionService and specifying the desired callback contract:

public interface IMyEvents { [OperationContract(IsOneWay = true)] void OnEvent1(); [OperationContract(IsOneWay = true)] void OnEvent2(int number); [OperationContract(IsOneWay = ...