Volodymyr Voytyshyn

03/17/2012

Managed

Extensibility Framework

Effective Development of Scalable Applications with .NET

Agenda

� What is MEF?

� Key concepts and features

� How to implement …?

� What’s new in MEF 2.0?

WHAT IS MEF?

The Problem

No unified approach

for extending applications in runtime

The Solution

�MEF – Managed Extensibility Framework

� Simply

� Reliably

� Unified

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)

MEF focuses on…

� extending of ready-made applications

Plugin 1 Plugin 2

Application

How about reflection?

System.Reflection .*

Assembly.Load ()

…

As a result…

� The next unique solution

� Not reusable components

� Extending by 3rd parties plugins

KEY CONCEPTS AND FEATURES

Composable Part

Part

Export

Import

More Composable Parts

ImportImport

ExportExport

The Main Idea - Composition

Composition Container

Composition Container

� Create parts

� Dispose parts

� Compose parts

Part Sample

Typed Contract

Part Sample

Named Contract

Part Sample

Extension

Point

Extension

Point

Composition of Parts

Composition

of parts

Don’t forget…

� Add reference

System.ComponentModel.Composition.dll

� Using namespaces

System.ComponentModel.Composition .*

More About Import

Export Metadata

Key

Value

Getting Exports from Container

Contract

Returns Lazy

Creation Policy

Default

value

� Shared

� NonShared

� Any

� Shared == Singleton

� Any & Any == Shared

References to Parts

� Container keeps reference to part if:

– Part is marked as Shared

– Part implements IDisposable

– One or more imports allow Recomposition

Disposing Composition Container

� Dispose parts which implement IDisposable

� Reference to parts will be cleaned up

� Lazy exports won’t work

Catalog

Catalog

Composition

Container

Discover

parts

Compose

parts

Catalog Types

Assembly Catalog

Directory Catalog

Type Catalog

Aggregate Catalog

Deployment Catalog

(only for Silverlight)

Recomposition Support

� Assembly Catalog

� Directory Catalog Refresh()

� Type Catalog

� Aggregate Catalog auto

� Deployment Catalog auto

HOW TO IMPLEMENT… ?

MEF-based Dependency Injection

Composition

Container

Service Locator

TPart Resolve <TPart>()

void Release <TPart>(TPart part) Common

Service Locator

MEF Adapter

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)

Plugin-based Desktop Application

Most Useful Tool

Directory

Catalog

Composition

Container

File System Watcher

Plugins Folder

Track

changes

Refresh()

Plugin-based Desktop Application

�Allow parts recomposition

�Assemblies shadow copy

! Plugin assembly

can not be unloaded in runtime

Plugin-based ASP.NET MVC Application

ASP.NET MVC Application

Models Views Plugins

Models Views

Plugin-based ASP.NET MVC Application

�Integrate MEF into ControllerFactory

�MEF-based DependencyResolver

? Compile razor view to separate assembly

WHAT’S NEW IN MEF 2.0?

MEF 2.0 and .NET 4.5

Open Generic Parts

Any type

Convention-based Part Registration

Composition Scoping Enhancements

Global Scope

Request Scope

Composition Container

Logger

Customer Controller

Customer RepositoryFor each request

Once

Composition Provider for ASP.NET MVC

� Registering in composition container:

– Controllers

– Action filters

– Model binders

� Constructor injection for controllers

ASP.NET MVC: processing of parts

Naming

convention

Contract

identification

Composition Provider for ASP.NET MVC

� Composition scopes

– Request scope

– Application scope

MEF Offers…

� Easy way for:

� Composition independent components

� Extending without recompiling

� Delivering 3rd party plugins

Ask your question…

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)

Thank You!

Copyright © 2011 SoftServe, Inc.

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