Managed Extensibility Framework (MEF) allows applications to be easily extended through extensions and plugins. MEF provides a composition container that discovers, loads, and composes parts through imports and exports. Key concepts include composable parts, imports, exports, and catalogs. MEF 2.0 introduced new features like open generic parts and convention-based registration to make MEF more powerful and flexible. MEF provides an easy way to build extensible applications using third party plugins and extensions.

1. Managed
Extensibility Framework
Effective Development of Scalable Applications with .NET
Volodymyr Voytyshyn
03/17/2012

2. Agenda
 What is MEF?
 Key concepts and features
 How to implement …?
 What’s new in MEF 2.0?

3. WHAT IS MEF?

4. The Problem
No unified approach
for extension application in runtime

5. The Solution
 MEF – Managed Extensibility Framework
 Simply
 Reliably
 Unified

6. MEF Project
 Official Site http://mef.codeplex.com
 Developer Microsoft
 Started 26.08.2008
 License MS Public License
(open source)
 Last stable release MEF 1 / 12.04.2010
(included into .NET 4.0)

7. MEF focuses on…
 Extending of ready-made applications by plugins
Application
Plugin 1 Plugin 2

8. How about reflection?
System.Reflection.*
Assembly.Load()
…

9. As a result…
 The next unique solution
 Not reusable components
 Extending by 3rd parties
plugins

10. KEY CONCEPTS AND FEATURES

11. Composable Part
Export
Part
Import

12. More Composable Parts
Import
Import
Export
Export

13. The Main Idea - Composition

14. Composition Container
Composition Container
 Compose parts
 Creates parts
 Dispose parts

15. The Part
Typed Contract

16. The Part
Named Contract

17. The Part
Extension
Point
Extension
Point

18. Composition of Parts
Composition
of parts

19. Don’t forget…
 Add reference
System.ComponentModel.Composition.dll
 Using namespaces
System.ComponentModel.Composition.*

20. More About Import

21. Export Metadata
Key
Value

22. Getting Exports
Contract
Returns Lazy

23. Creation Policy
 Shared
Default
 NonShared value
 Any
 Any & Any == Shared
 Shared == Singleton

24. References to Parts
 Container keeps reference to part if:
– Part is marked as Shared
– Part implements IDisposable
– One or more imports allow Recomposition

25. Disposing Composition Container
 Dispose parts which implement IDisposable
 Reference to parts will be cleaned up
 Lazy exports won’t work

26. Catalog
Composition
Container
Compose
parts
Discover
parts
Catalog

27. Catalog Types
Assembly Catalog
Directory Catalog
Type Catalog
Aggregate Catalog
Deployment Catalog
(only for Silverlight)

28. Recomposition Support
 Assembly Catalog
 Directory Catalog Refresh()
 Type Catalog
 Aggregate Catalog auto
 Deployment Catalog auto

30. HOW TO IMPLEMENT… ?

31. MEF-based Dependency Injection
Service Locator
TPart Resolve<TPart>()
void Release<TPart>(TPart part) Common
Service Locator
Composition
Container MEF Adapter

32. MEF vs IoC
+ Ease of programming
+ Resolves dependencies between components
+ Automatic component discovery
+ Can compose types, fields, props and methods
- Slower than IoC containers
- Poor component lifetime management
- No component separation (separate appdomain, process)

33. Plugin-based Desktop Application
Most Useful Tool
Composition
Container Plugins Folder
Directory
Catalog
Refresh()
Track
File System Watcher
changes

34. Plugin-based Desktop Application
 Allow parts recomposition
 Assemblies shadow copy
! Plugin assembly
can not be unloaded in runtime

35. Plugin-based ASP.NET MVC Application
ASP.NET MVC Application
Models Views Plugins
Models Views

36. Plugin-based ASP.NET MVC Application
Integrate MEF into ControllerFactory
MEF-based DependencyResolver
? Compile razor view to separate assembly

37. WHAT’S NEW IN MEF 2.0?

38. MEF 2.0 and .NET 4.5

39. Open Generic Parts
Any type

40. Convention-based Part Registration

41. Composition Scoping Enhancements
Once Global Scope
Logger
Composition Container
Request Scope
Customer Controller
For each request Customer Repository

42. Composition Provider for ASP.NET MVC
 Registering in composition container:
– Controllers
– Action filters
– Model binders
 Constructor injection for controllers

43. ASP.NET MVC: processing of parts
Naming
convention
Contract
identification

44. Composition Provider for ASP.NET MVC
 Composition scopes
– Request scope
– Application scope

45. MEF Offers…
 Easy way for:
 Composition independent components
 Extending without recompiling
 Delivering 3rd party plugins

46. Ask your question…

47. Useful Sources
 MEF Project (official site)
 Managed Extensibility Framework Overview (msdn)
 Building Composable Apps in .NET 4 with MEF (msdn)
 BCL Team Blog (msdn)
 Book of MEF (habrahabr)

48. Contacts
Volodymyr Voytyshyn
5 Knyahyni Olhy Str., Rivne 33000, Ukraine
Tel: +38(066) 41 83 509
E-mail: vvoit@softserveinc.com
voytyshyn@gmail.com
Skype: voytyshin
Thank You!
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