The Moth

Anybody that has built an application that supports AddIns (aka add-in, plug-in, etc) knows that there are many design decisions to make and quite a few subtleties in implementing those decisions in particular when it comes to discovering addins, version resiliency, isolation from the host etc.

In NetFx 3.5 (part of "Orcas"), a whole bunch of classes do all this work on your behalf and all you have to do is make simple method calls to configure the behaviour. These new types are in the following namespaces: System.AddIn, System.AddIn.Hosting, System.AddIn.Pipeline and System.AddIn.Contract.

The implementation was part of System.Core.dll in early CTPs; starting with the March CTP they reside in their own assembly: System.AddIn.dll (be sure to reference the System.AddIn.dll from v3.5 residing in "C:\Windows\Microsoft.NET\Framework\v3.5.20209", not the one from v2.0 that appears in the References dialog by default).

To learn more about how to use the new AddIn model, please read the two part msdn magazine article (part one and two). Also check out the AddIn blog where you can learn about internal implementation decisions that could help you with the add-in infrastructures that you build today! For a real example of the AddIn classes, see this blog series that describes how Paint.NET is being refactored to take advantage of the new plumbing.