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Managed Extensibility Framework (MEF)

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Mohamed Meligy
Mohamed Meligy

The document discusses the Managed Extensibility Framework (MEF), a library developed by Microsoft that allows applications and components to be extended through extensions. MEF allows developers to easily discover and use extensions with their applications through a simple yet powerful composition model. Examples are provided of how MEF allows applications and components to be flexibly extended through external plug-ins and modules.

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Managed Extensibility Framework (MEF) Mohamed Meligy Code: 02F01
Extensibility Extensions
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DI is all about wiring up objects Come on, that isn’t hard. We’ve been doing that for years!
Web App Stock Quotes Authenticator Error Handler Logger Database This example was created by Jim Weirich in Ruby on his blog. See his original article http ://onestepback.org/index.cgi/Tech/Ruby/DependencyInjectionInRuby.rdoc
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How does the StockQuotes find the Logger? How does the Authenticator find the database? Etc.? Suppose you want to use a TestingLogger instead? Or a MockDatabase?
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public class MyLocator : ILocator { protected Dictionary<Type, object> dict = new Dictionary<Type,object>(); public MyLocator() { dict.Add(typeof(ILogger), new Logger()); dict.Add(typeof(IErrorHandler), new ErrorHandler(this)); dict.Add(typeof(IQuotes), new StockQuotes(this)); dict.Add(typeof(IDatabase), new Database(this)); dict.Add(typeof(IAuthenticator), new Authenticator(this)); dict.Add(typeof(WebApp), new WebApp(this)); } }
public class StockQuotes { public StockQuotes(ILocator locator) { errorHandler = locator.Get<IErrorHandler>(); logger = locator.Get<ILogger>(); } // More code here... }
Classes are decoupled from explicit imlementation types Easy to externalize the config
Everyone takes a dependency on the ILocator Hard to store constants and other useful primitives Creation order is still a problem
Gets rid of the dependency on the ILocator Object is no longer responsible for finding its dependencies The container does it for you
Write your objects the way you want Setup the container Ask the container for objects The container creates objects for you and fulfills dependencies
DIContainer container = new DIContainer(); container.Register<ILogger, Logger>(); container.Register<IDatabase, Database>(); container.Register<IErrorHandler, ErrorHandler>(); container.Register<IQuotes, StockQuotes>(); container.Register<IAuthenticator, Authenticator>(); container.Register<IWebApp, WebApp>();
Ìý
Ìý
To Singleton or Not to Singleton? Nested Containers Property Setter Object Lifetime Method Invocation Event Wire-up Instrumentation Method Interception via Dynamic Proxies
Spring.NET Castle Windsor StructureMap Microsoft Unity (Enterprise Library) MEF ?????
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Hard to enable, hard to create Many extensibility models Extensibility Extending the extensions 2
Application ToolWindow A ToolWindow B Contacts Call Support Help File Edit View Tools Help
Application Extension A Extension B Need a Toolwindow Got a Toolwindow Need Menus Got a Menu Need a MenuService Got a MenuService
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Windows And Menus With MEF public interface IToolWindow { } public interface IMenuService { }Ìý public interface IMenu { } Ìý public class Application { [ Import ] public IEnumerable < IToolWindow > ToolWindows { get ; set ; } Ìý [ Import ] public IEnumerable < IMenu > Menus { get ; set ; } } Ìý [ Export ( typeof ( IMenuService ))] public class MenuService : IMenuService { }
Windows And Menus With MEF [ Export ( typeof ( IToolWindow ))] public class SomeToolWindow : IToolWindow { [ Import ] public IMenuService MenuService { get ; set ; } } Ìý [ Export ( typeof ( IMenu ))] public class SomeMenu : IMenu {} Ìý
First, The Composable Part Part A
Parts Relate Through Contracts Part B Part A
Imports Are Contracts A Part Needs Part B Import Import
Exports Are Contracts A Part Offers Export Export Part B
The Container Is The Matchmaker Container
Container Queries Catalogs Catalog Container
Parts Can Load Lazily Part B Part A Export <A>
Parts Can Have Different Lifetimes Container Container Part A Singleton Part A Part A Part A Factory
Ìý
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Part of the framework Microsoft will use it Developers will use it Write add-ins Create extensible apps Microsoft has not decided
http://www.codeplex.com/MEF MEF Home http://tinyurl.com/MEFGuide Programming Guide http://tinyurl.com/MEFDiscussions Discussions http://tinyurl.com/MEFBlogs Team Blogs http://channel9.msdn.com/pdc2008/TL33/ MEF @ PDC 2008 http://blogs.msdn.com/gblock/ Glenn Block, The MEF Guy Code: 02F01 Eng . [email_address] . com weblogs . asp . net/meligy
MEF Preview 4 Source Code & Samples http://www.codeplex.com/MEF/Release/ProjectReleases.aspx?ReleaseId=22313 MEF Article Formatter Sample http://blogs.conchango.com/robhenry/archive/2008/11/11/managed-extensibility-framework-mef.aspx MEF Grid Sample http://blogs.msdn.com/dsplaisted/archive/2009/01/14/mefgrid-a-sample-mef-application.aspx

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Managed Extensibility Framework (MEF)

  • 1. Managed Extensibility Framework (MEF) Mohamed Meligy Code: 02F01
  • 4. DI is all about wiring up objects Come on, that isn’t hard. We’ve been doing that for years!
  • 5. Web App Stock Quotes Authenticator Error Handler Logger Database This example was created by Jim Weirich in Ruby on his blog. See his original article http ://onestepback.org/index.cgi/Tech/Ruby/DependencyInjectionInRuby.rdoc
  • 7. How does the StockQuotes find the Logger? How does the Authenticator find the database? Etc.? Suppose you want to use a TestingLogger instead? Or a MockDatabase?
  • 9. public class MyLocator : ILocator { protected Dictionary<Type, object> dict = new Dictionary<Type,object>(); public MyLocator() { dict.Add(typeof(ILogger), new Logger()); dict.Add(typeof(IErrorHandler), new ErrorHandler(this)); dict.Add(typeof(IQuotes), new StockQuotes(this)); dict.Add(typeof(IDatabase), new Database(this)); dict.Add(typeof(IAuthenticator), new Authenticator(this)); dict.Add(typeof(WebApp), new WebApp(this)); } }
  • 10. public class StockQuotes { public StockQuotes(ILocator locator) { errorHandler = locator.Get<IErrorHandler>(); logger = locator.Get<ILogger>(); } // More code here... }
  • 11. Classes are decoupled from explicit imlementation types Easy to externalize the config
  • 12. Everyone takes a dependency on the ILocator Hard to store constants and other useful primitives Creation order is still a problem
  • 13. Gets rid of the dependency on the ILocator Object is no longer responsible for finding its dependencies The container does it for you
  • 14. Write your objects the way you want Setup the container Ask the container for objects The container creates objects for you and fulfills dependencies
  • 15. DIContainer container = new DIContainer(); container.Register<ILogger, Logger>(); container.Register<IDatabase, Database>(); container.Register<IErrorHandler, ErrorHandler>(); container.Register<IQuotes, StockQuotes>(); container.Register<IAuthenticator, Authenticator>(); container.Register<IWebApp, WebApp>();
  • 16. Ìý
  • 17. Ìý
  • 18. To Singleton or Not to Singleton? Nested Containers Property Setter Object Lifetime Method Invocation Event Wire-up Instrumentation Method Interception via Dynamic Proxies
  • 19. Spring.NET Castle Windsor StructureMap Microsoft Unity (Enterprise Library) MEF ?????
  • 20. Ìý
  • 21. Ìý
  • 22. Hard to enable, hard to create Many extensibility models Extensibility Extending the extensions 2
  • 23. Application ToolWindow A ToolWindow B Contacts Call Support Help File Edit View Tools Help
  • 24. Application Extension A Extension B Need a Toolwindow Got a Toolwindow Need Menus Got a Menu Need a MenuService Got a MenuService
  • 25. Ìý
  • 26. Windows And Menus With MEF public interface IToolWindow { } public interface IMenuService { }Ìý public interface IMenu { } Ìý public class Application { [ Import ] public IEnumerable < IToolWindow > ToolWindows { get ; set ; } Ìý [ Import ] public IEnumerable < IMenu > Menus { get ; set ; } } Ìý [ Export ( typeof ( IMenuService ))] public class MenuService : IMenuService { }
  • 27. Windows And Menus With MEF [ Export ( typeof ( IToolWindow ))] public class SomeToolWindow : IToolWindow { [ Import ] public IMenuService MenuService { get ; set ; } } Ìý [ Export ( typeof ( IMenu ))] public class SomeMenu : IMenu {} Ìý
  • 28. First, The Composable Part Part A
  • 29. Parts Relate Through Contracts Part B Part A
  • 30. Imports Are Contracts A Part Needs Part B Import Import
  • 31. Exports Are Contracts A Part Offers Export Export Part B
  • 32. The Container Is The Matchmaker Container
  • 33. Container Queries Catalogs Catalog Container
  • 34. Parts Can Load Lazily Part B Part A Export <A>
  • 35. Parts Can Have Different Lifetimes Container Container Part A Singleton Part A Part A Part A Factory
  • 36. Ìý
  • 37. Ìý
  • 38. Part of the framework Microsoft will use it Developers will use it Write add-ins Create extensible apps Microsoft has not decided
  • 39. http://www.codeplex.com/MEF MEF Home http://tinyurl.com/MEFGuide Programming Guide http://tinyurl.com/MEFDiscussions Discussions http://tinyurl.com/MEFBlogs Team Blogs http://channel9.msdn.com/pdc2008/TL33/ MEF @ PDC 2008 http://blogs.msdn.com/gblock/ Glenn Block, The MEF Guy Code: 02F01 Eng . [email_address] . com weblogs . asp . net/meligy
  • 40. MEF Preview 4 Source Code & Samples http://www.codeplex.com/MEF/Release/ProjectReleases.aspx?ReleaseId=22313 MEF Article Formatter Sample http://blogs.conchango.com/robhenry/archive/2008/11/11/managed-extensibility-framework-mef.aspx MEF Grid Sample http://blogs.msdn.com/dsplaisted/archive/2009/01/14/mefgrid-a-sample-mef-application.aspx