1. Crystal MEF

2. Software is Hard 
• Components
• Extensibility
– IDTExtensibility2
– ASP.NET Providers
– System.AddIn

3. Managed Extensibility Framework
• Released under .NET 4.0
– System.ComponentModel.Composition
• Open source
– http://mef.codeplex.com
• DEMOS

4. 4(½) Key Concepts
• Parts
– A component that does something
• Export
– Parts that are available to be consumed
• Import
– Parts that a program consumes
• Composition
– The process by which Imports and Exports are
mated together

5. 1. Parts
• A type annotated with MEF metadata

6. 2. Export
• [Export] on a class exposes it as a Part
[Export]
public class Logger()
…
• [Export(type)] can expose a specific type e.g.
an interface
[Export(typeof(ILogger)
public class Logger :Ilogger
• [Export(string)] can expose a named
contract

7. 3. Import
• [Import(type)] on a property makes it
consume a Part
public class SomeClass
[Import(typeof(Ilogger))
private Ilogger MyLogger()
• [ImportMany()] allows a part to import a
collection (IEnumerable<T>) of parts

8. 4. Composition
• Parts are loaded through Catalogs
– TypeCatalog
• IEnumerable<types>
• [types]
– AssemblyCatalog
– DirectoryCatalog
– Your custom implementation of a catalog e.g.
DatabaseCatalog, DownloadCatalog

9. ½. Recomposition
• Dynamic composition in response to a change
in the number of available Parts

10. MEF Help
• No book 
• http://tinyurl.com/stackoverflowmef
• Twitter
– @gblock
– @kathleendollard
– #MEF