The Managed Extensibility Framework (MEF) improves the flexibility, maintainability, and testability of large .NET applications by providing a composition layer for plugin extensibility or a loosely-coupled architecture. MEF is part of the .NET Framework and uses parts (objects that import or export values) and a composition container that uses catalogs of parts to perform composition by binding imports to exports. Imports and exports allow components to communicate by specifying needs or availability of values through contracts.

1. The Managed ExtensibilityFramework(MEF) isa compositionlayerfor.NETthatimprovesthe
flexibility,maintainabilityandtestabilityof large applications.MEFcan be usedforthird-partyplugin
extensibility,oritcan bringthe benefitsof a loosely-coupledplugin-like architecture toregular
applications.
MEF isa part of the Microsoft .NETFramework,withtypesprimarilyunderthe System.Composition.
Namespaces.There are twoversionsof MEF
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MEF isan integral partof the .NET Framework4, andis available whereverthe .NETFrameworkis
used.Youcan use MEF in yourclientapplications,whethertheyuse WindowsForms,WPF,orany
othertechnology,orinserverapplicationsthatuse ASP.NET.
Parts andthe compositioncontainerare the basicbuildingblocksof aMEF application.A partis any
objectthat importsorexportsa value,upto andincludingitself.A catalogprovidesacollectionof
parts froma particularsource.The compositioncontainerusesthe partsprovidedbyacatalogto
performcomposition,the bindingof importstoexports.
Importsand exports
Importsand exportsare the wayby whichcomponentscommunicate.Withanimport,the
componentspecifiesaneedforaparticularvalue or object,andwithan exportitspecifiesthe
availabilityof avalue.Eachimportis matchedwitha listof exportsbywayof itscontract.