Question

Folks,

I have a feeling there’s a classic design pattern that covers this case, but I don’t have a reference handy.

I have a situation where a user clicks a button and another part of the web page responds. What’s unusual (or at least inconvenient) is that the button and the reponding part of the web page are in very different control hierarchies, both in terms of distance to common ancestor and in terms of application concern. They’re both inner parts of a series of (separate) black boxes.

I have not been able to come up with an elegant way for the one to trigger the other. I do not want to have to raise a series of events up to the top of the control hierarchy and then call a series of nested methods to make the desired effect happen. (“effect” != visual effect; I can’t solve this with jQuery) I want the event and the responder to remain ignorant of each other: I will not violate separation of concerns by having the latter know about and directly subscribe to an event generated by the former. I’ve considered a number of other inelegant solutions, but I won’t bore you by listing them off.

Basically I guess I need a way to implement a publisher-subscriber model for events in which anything can subscribe to anything.

I’m using .Net 4.0. Any nice frameworks that do this? Any easy ways to implement it?

Thanks a lot,

Ann L.

Answer 1

Sounds like you need an EventAggregator. You should find the implementation in the Composite Application Library.

The EventAggregator allows you to register to notifications and raise them from completely separated parts of the application.