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 extending applications 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
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
Create parts
Dispose parts

15. Part Sample
Typed Contract

16. Part Sample
Named Contract

17. Part Sample
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 from Container
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!
Copyright © 2011 SoftServe, Inc.