MEF in Silverlight 4 - a guided tour
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The document is a comprehensive guide to the Managed Extensibility Framework (MEF) in Silverlight 4, detailing its purpose as an extensible framework for composing applications from loosely-coupled parts. It explains key concepts such as inversion of control (IoC), composition, and the role of catalogs and parts in application development. The document also highlights the benefits of using MEF, including improved testability and dynamic recomposition of parts, alongside examples and practical scenarios.
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MEF in Silverlight 4 - a guided tour
- 1. MEF in Silverlight 4 – a guided tourMike TaultyMicrosoft Ltdmtaulty@microsoft.commtaulty.comtwitter.com/mtaulty
- 2. [background]
- 3. MEF – What is it? How do I get it?the Managed Extensibility Frameworkan extensible framework for composing applications from a set of loosely-coupled parts discovered and evolving at run-time versions.NET Framework shipping with Silverlight 4 .NET Framework 4 shipping with VS 2010Silverlight 3 & .NET Framework V3.5 Sp1Source on CodePlex
- 4. “scenario”iTunesMediaPlayerConstructor()GetAlbumInfo(“Blood on the Tracks”)IAlbumInfoProviderAlbumInfoProviderConstructor()GetAlbumArt(“Blood on the Tracks”)IAlbumArtProviderAlbumArtProvider
- 5. “scenario”iTunesMediaPlayerConstructor()GetAlbumInfo(“Blood on the Tracks”)AlbumInfoProviderConstructor()GetAlbumArt(“Blood on the Tracks”)AlbumArtProviderStatic dependency AlbumInfoProvider->AlbumArtProvider
- 6. Hard to test AlbumInfoProvider in isolation from AlbumArtProvider
- 7. Hard to drop in a different AlbumArtProvider implementation
- 8. Code changes to AlbumArtProvider impact AlbumInfoProviderInversion of Control ( IoC )iTunesMediaPlayerIAlbumArtProviderConstructor()Works ok for the single dependency case but this won’t scale to trees of objects of arbitrary complexityAlbumArtProviderAlbumArtProviderConstructor(IAlbumArtProvider)GetAlbumInfo(“Blood on the Tracks”)AlbumInfoProviderGetAlbumArt(“Blood on the Tracks”)Static dependency AlbumInfoProvider->IAlbumArtProvider
- 9. Easier to test AlbumInfoProvider with anyIAlbumArtProvider
- 10. Easier to drop in new implementations of IAlbumArtProvider
- 11. Version changes to AlbumArtProvider do not impact AlbumInfoProviderthe IoC Container“RegisterMapping “typeof(IAlbumArtProvider) typeof(AlbumArtProvider)“RegisterMapping “typeof(IAlbumInfoProvider) typeof(AlbumInfoProvider)Container
- 14. example ( Unity IoC )
- 15. but MEF is not ‘just’ another IoC containeran extensible framework for composing applications from a set of loosely-coupled parts discovered and evolving at run-time
- 16. using MEF in our scenariodemo
- 17. MEF models composable partsimportimportimportPartexportexport
- 18. MEF composes partsimportimportimportimportimportimportimportpartpartpartpartimportimportexportexportexportComposition Engineexportpartpartpartpartpart
- 19. which parts compose together?importimportimportpartexportexport?importpart
- 20. matching imports to exportsdemo
- 21. parts & part definitionsimportimportimportimportPartPartDefinitionCreatePart()exportexportexportPartDefinition is a blueprint for a Partsimilar to Object and Type in .NETbut can have Part without PartDefinition
- 22. container draws parts from catalogsPartDefinitionPartDefinitionPartDefinitionPartDefinitionPartDefinitionPartDefinitionPartDefinitionPartDefinitionPartDefinitionimportimportimportPartDefinitionimportimportimportPartDefinitionimportimportimportPartDefinitionPartPartPartCatalogCatalogCatalogexportexportexportexportexportexportCatalogCompositionContainer
- 23. or mix in pre-instantiated partspartImports(“Foo”)Compose()partExports(“Foo”)CompositionContainer
- 25. things change - recompositionNew parts [introduced to/removed from] container may have an impact on this import – a part can opt-in to allow this recompositionpartCompose()part?partCompositionContainerpartCatalogCatalogCatalogPartDefinitionPartDefinitionPartDefinitionPartDefinitionSome catalogs support additions
- 26. recomposition is key for Silverlightinitial, small downloadMyApp.xapExtras.xapadditional functionality
- 27. recomposition & the DeploymentCatalogdemo
- 28. stable compositionreject parts with unsatisfied importsreject changes that break existing “agreements”partpartrequires exactlyone partrequirespartpartrequiresCompositionContainermissingdifferent part,same contractpart
- 30. MEF and Model View ViewModelStrong separation of concerns possible with Silverlight developmentuser interface declared in XAMLloosely binds to datafunctionality invoked by declarative commandsEncapsulated by the “MVVM” patternbindingmodel(“data”)viewmodel(state & data for view)view(declarative XAML)commands
- 31. MVVM via MEFdemo
- 32. resourcesGlenn Blockblogs.msdn.com/gblockNicholas Blumhardtblogs.msdn.com/nblumhardtMEF on CodePlexmef.codeplex.comChannel 9 Silverlight 4 MEF Screencastschannel9.msdn.com/tags/learnMEFSL4
- 33. feedbackMicrosoft Session Feedback via Twitter@msftsession 10 @mtaulty #sluguk ...session score out of 10( 10 is recommended but other scores are possible )