Introduction to the Managed Extensibility Framework in Silverlight
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This document provides an introduction to the Managed Extensibility Framework (MEF) using Silverlight. It discusses why MEF is useful for discovery, lifetime management, and extensibility. It also highlights 10 practical reasons to use MEF, such as providing inversion of control and allowing for multiple implementations of contracts. The document includes code demos to illustrate concepts like importing many implementations, using MEF with MVVM, dynamic XAP file loading, and filtering with metadata.
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Introduction to the Managed Extensibility Framework in Silverlight
- 1. Intro to MEF with Silverlight Jeremy Likness Project Manager, Senior Consultant jlikness@wintellect.com Copyright © 2011 consulting training design debugging wintellect.com
- 2. what we do consulting training design debugging who we are Founded by top experts on Microsoft – Jeffrey Richter, Jeff Prosise, and John Robbins – we pull out all the stops to help our customers achieve their goals through advanced software-based consulting and training solutions. how we do it Training • On-site instructor-led training Consulting & Debugging • Virtual instructor-led training • Architecture, analysis, and design services • Devscovery conferences • Full lifecycle custom software development • Content creation Design • Project management • User Experience Design • Debugging & performance tuning • Visual & Content Design • Video & Animation Production consulting training design debugging wintellect.com
- 3. Agenda • Why MEF? • Discovery • Lifetime Management • Extensibility • Metadata • 10 Practical Reasons to use MEF consulting training design debugging wintellect.com
- 4. Why MEF? • Misconception: Managed Extensibility Framework • Part of the framework • Discovery • Lifetime management • Extensibility • Metadata consulting training design debugging wintellect.com
- 5. Welcome to the MEF Lab! • I admit I am a MEF addict! • You may be surprised by who has done MEF • Visual Studio 2010 • 2010 Vancouver Olympics • Microsoft (Looking Glass) • SharePoint consulting training design debugging wintellect.com
- 6. Discovery • Import: Contract and Demand • Export: Implementation and Supply Look Ma! I • Part: Supply & Demand need 500 don’t constructor overloads! “I need something that implements IMessage” [Import] public IMessage MyMessenger { get; set; } [Export(typeof(IMessage))] public class SpecificMessenger : IMessage “I have something that implements IMessage” consulting training design debugging wintellect.com
- 7. Discovery: Catalogs • Catalogs tell MEF where to find parts • AssemblyCatalog: Current assembly • TypeCatalog: List of types • DeploymentCatalog: Silverlight XAP file • AggregateCatalog: Composed of Multiple Catalogs consulting training design debugging wintellect.com
- 8. Discovery: Container • The Container wraps the Catalog • The Container is responsible for Composition: – What parts exist? • What imports exist for a part? • What exports exist for a part? • This is the Discovery step • In Silverlight specifically the “CompositionInitializer” handles containers consulting training design debugging wintellect.com
- 9. Discovery: Catalogs & Containers Wraps parts in the current XAP Look Ma! No var deploymentCatalog = new DeploymentCatalog(); var container = new Bootstrapper! CompositionContainer(deploymentCatalog); container.ComposeParts(this); Using the parts in the container, find all parts in the current class, then satisfy all imports with corresponding exports (“Composition”) consulting training design debugging wintellect.com
- 10. Demo Hello, MEF! consulting training design debugging wintellect.com
- 11. CompositionInitializer • Notice that composition happens “explicitly” with the composition call • What about XAML objects? These are created by the XAML parser, not MEF • How do you share a container across the application? • CompositionInitializer solves this problem by creating a default, global container • Must be high level: classes that use this cannot export themselves! consulting training design debugging wintellect.com
- 12. Stable Composition • Guarantees imports are satisfied • Works throughout the entire hierarchy • Helps keep plug-ins “honest” • What about multiple plug-ins? consulting training design debugging wintellect.com
- 13. ImportMany • Allows multiple implementations • Stable composition will reject invalid exports consulting training design debugging wintellect.com
- 14. Demo ImportMany consulting training design debugging wintellect.com
- 15. Lifetime Management • What’s wrong with Singletons? – Change the behavior of the class simply to modify the lifetime of the class (poor separation of concerns) – Tough to test and mock – Often abused and create dependencies • PartCreationPolicy • RequiredCreationPolicy • Factory consulting training design debugging wintellect.com
- 16. Demo MVVM & Lifetime Management consulting training design debugging wintellect.com
- 17. Bonus: Design and Test with MEF • Use composition for the run time • Use design prefixes for design-time – Composition will fail in the designer due to a different runtime for Cider, but this is fine if you follow the pattern described – Use mock utilities that can mock an object for the interface • In test, you can export a different implementation or simply set mocks directly consulting training design debugging wintellect.com
- 18. Extensibility • Most inversion of control/dependency injection frameworks help wire what you know (bootstrapper) • MEF provides for what you don’t know • For non-extensible applications, this still allows for modularity • For extensible applications, this allows for plug-ins consulting training design debugging wintellect.com
- 19. Extensibility: Dynamic XAP Files • First, use an AggregateCatalog to allow multiple XAP files • The DeploymentCatalog allows asynchronous downloads for XAP files • Use a new Silverlight Application to create satellite assemblies • CompositionHost will override the default container • CopyLocal = false for duplicate references • AllowRecomposition • ObservableCollection consulting training design debugging wintellect.com
- 20. Demo Dynamic XAP File consulting training design debugging wintellect.com
- 21. Metadata • Add additional information about an export • Filter exports without invoking/creating them • Allows for plug-ins to only be generated in context • Strongly typed • Uses the pattern Lazy<T,TMetadata> consulting training design debugging wintellect.com
- 22. Demo Metadata with Jounce consulting training design debugging wintellect.com
- 23. 10 Practical Reasons to Use MEF 1. It’s out of the box 2. It provides Inversion of Control/Discovery 3. It gives you lifetime management 4. It can easily manage application wide configuration 5. It provides factories that resolve their own dependencies 6. It allows for multiple implementations of the same contract (pipeline and chain of responsibility) 7. It filters with strongly-typed metadata 8. It dynamically loads modules and extends existing applications 9. It provides for modularity and clean separation of concerns 10. It is completely customizable to address your specific needs (i.e. ExportFactory) consulting training design debugging wintellect.com
- 24. Questions? Jeremy Likness Project Manager, Senior Consultant jlikness@wintellect.com consulting training design debugging wintellect.com
Editor's Notes
- I’ve been talking about MEF for awhile. At many of my talks, I’m stopped with “Jeremy, hold on, you’re showing us advanced uses of MEF. But why do I even want to use MEF in the first? What is it exactly that MEF does?”
- Discovery is what most people are looking to do when they implement Inversion of Control and Dependency Injection. There are many ways to do discovery from factories and service locators to bootstrappers and IoC containers. MEF provides a very simple and straightforward way to handle discovery.
- Copy the Hello MEF. Convert to a ListBox. Change Text to an array and then set the items source.
- Creation policies are run always once, when the imports are satisfied. Factory is unique in that it provides a means for creating new instances, and works independent of the part creation policy.
- This demo is a full-fledged MEF/MVVM solution. It shows not only the lifetime management concept, but how MEF works with MVVM to drive Silverlight applications. It also shows design-time support with MEF.
- Copy the import many. Add an aggregate catalog and use that in the container and introduce CompositionHost. Disable the button on click. Change the text to an observable collection, then add the new project with the export. Show that the button click does NOT actually pull the new export. Then add AllowRecomposition and show it working.
- Jounce is a framework that provides specific guidance for MVVM with MEF.
- If time permits, go back to some of the case studies and discuss how they worked with MEF.