MEF (Managed Extensibility Framework) is a framework for creating extensible applications that focuses on discovery of parts at runtime. It allows for exposing and importing functionality through composable parts defined with attributes. Catalogs define which parts are available to the system and can be filtered. The composition container wires everything together and satisfies dependencies. Export providers determine the lifetime of parts as shared, non-shared, or any. MEF demonstrates composition, filtering, recomposition, and creation policies through examples. While MEF puts components together, it is not an inversion of control container that defines dependencies.

1. MEFilicious Applications
Owen Evans
Developer - Xero
@buildmaster http://bgeek.net

2. What is MEF
• Managed Extensibility Framework
• Standards for exposing yourself!
• Open/Closed principal
• It’s all so META

6. ComposablePart
• The building block of a MEF enabled
application
• Defines an [Import] or [Export] (or
both)

7. Catalog - a collection of
parts
• Catalogs are how you define which parts
are available to the system
• Directory Catalog
• Assembly Catalog
• Aggregate Catalog

8. CompositionContainer
• Similar to an IoC container
• Wires everything together and satisfies
dependancies

9. demo time...
MEF 101

10. MEF steps
• Create a catalog (or collection of catalogs)
var catalog = new AggregateCatalog(new DirectoryCatalog(@"."),new
AssemblyCatalog(Assembly.GetExecutingAssembly()));
• Add catalog(s) to container
var container = new CompositionContainer(catalog);
• Get a type from the container
var window = container.GetExportedValue<CashMaker>();

11. Filtering
• Catalogs can be filtered down using a
FilteredCatalog*
(* source code available here: http://bit.ly/
MEFFilter)

12. demo time...
Filtered Catalog

13. Recomposition
• Import points can be marked as
recomposable
• New instances in the catalog matching
the import will cause the collection to be
rebuilt

14. demo time...
Recomposition

15. Lifetime
• Export providers can decide on the lifetime
of their parts:
• Shared: only one instance per container
• NonShared: each export will create a
new instance
• Any: allows any use (can be defined on
import)

16. demo time...
Creation Policy

17. Thats all there is to
MEF

18. MEF is:
• A framework for creating extensible
applications
• Puts focus on discovery of parts at run
time
• as such...

19. MEF is not
• IoC
• Inversion of Control is about knowing what
dependancies satisfy given classes and allowing the
class to hand this requirement off
• IoC containers are great at saying => “When asking
for an IDependancy you should get Dependancy”
• MEF doesn’t have a way of doing this
• MEF says I have all these objects and you want
some of them... HERE.

20. Did I say I’m running a Web Dev Conference?
http://wdcnz.com