COM & .NET Component Services

COM+ Event Model

The COM+ event model is based on a simple idea—put the connection setup and the event firing plumbing outside the scope of the components. Under COM+, an object that fires events is called a publisher . A client who wants to receive events is called a subscriber . Subscribers who want to receive events register with COM+ and manage the subscribe/unsubscribe process via COM+, not the object. Similarly, publishers hand over the events to COM+, not directly to the subscribed clients.

COM+ delivers an event to the clients that have subscribed. By having this layer of indirection, COM+ decouples your system. Your clients no longer have any knowledge about the identity of the publishers. The subscription mechanism is uniform across all publishers, and the publishers do not manage lists of connections.

The rest of this chapter explains the details of the COM+ events service, its capabilities and limitations, and its interaction with other COM+ services.