Silverlight Asynchronous WCF Calls Without Ruining Your Architecture

A while back I wrote a blog post about how Silverlight 4’s asynchronous network calls make a layered client-side architecture difficult.  In that post I talk about wanting to have a loosely coupled, testable, n-tier architecture on my Silverlight client application.  Basically, I wanted to have a client-side architecture that was nicely layered like Figure 1 rather than a flat, 1-tier