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Introduction of Managed Extensibility Framework (MEF)

, 3 Apr 2010 CPOL 27.5K 292 20
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An introduction of Managed Extensibility Framework (MEF) with Visual Studio 2010

Background

Software requirements evolve because of ever evolving businesses they are developed for. This evolution is making the life of software architects and designer ever more difficult. Modern software should be extensible. This is kind of Addins support in our applications. But available software tools lacked good provision of creating extensible applications. As good software architects and developers, we are always in the quest of getting this out of the box so that we can focus more on the business requirements.

Introduction

With Visual Studio 2010, Microsoft has introduced a great framework which must be looked at. This is called MEF (Managed Extensions Framework). This is based on the same software principles that were the basis of Inversion of Control pattern. We design software components in a way that they follow “Low Coupling” GRASP (General Responsibility Assignment Software Pattern) pattern.

Jump to Writing Code

Since I don’t want to waste anymore of your time, I am starting to create an example “Hello World” program using MEF. Let us create a Console C# Application. We name our application as MEFIntro.

CreateProject.JPG

Now we add a reference of System.ComponentModel.Composition.dll.

AddReference1.JPG

It is shown in the Solution explorer as follows:

AddRefernce2.JPG

Now we add the namespaces we need to create our first application in Program.cs.

using.JPG

We implement two classes in our namespace MEFIntro. They are as follows:

  1. Program(Listing 1)
  2. SimpeHello (Listing 2)

Dependencies in MEF are provided using attributes. There are two basic attributes. They are Import and Export. If you look at Programclass in Listing 1, you can figure out that, its string Property message should be importing some string. It doesn’t specify what would be the source of this import. Now in Listing 2, SimpleHelloexports some string property. Some other component might need this property. In our example, this is Programclass. So it is apparent that both these classes depend on each other.

Now if we just follow cowboy coding, we would directly instantiate MyHelloin Programclass and use MyHello.Messageproperty to populate its own Messageproperty. But, with MEF, we don’t need to do that. This is because MEF takes care of injecting the dependencies.

To determine the dependencies between software components, catalogs are defined (Runmethod in Programclass). Here we have used AssemblyCatalog. There may be more than one catalog of same or different types. There might be other catalogs too, like DirectoryCatalog, etc. After adding these catalogs in CompositionContainer, when we call ComposePartsmethod of the container, all dependencies are resolved. As you can see that when we call ComposeParts, stringproperty Messagein MyHelloclass (specified with Exportattribute) is copied to the stringproperty Messagein Programclass (specified with Importattribute).

Listing 1

class Program
{
    [Import]
    public string Message { get; set; }

    static void Main(string[] args)
    {
        Program p = new Program();
        p.Run();
    }

    public void Run()
    {
        var catalog = new hosting.AssemblyCatalog(Assembly.GetExecutingAssembly());
        var container = new hosting.CompositionContainer(catalog);
        container.ComposeParts(this);
        Console.WriteLine(Message);
        Console.ReadKey();
     }
}

Listing 2

public class MyHello
{
   [Export]
   public string Message
   {
       get { return "Hello World"; }

   }
}

History

  • 03/03/2010: Article posted

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Muhammad Shujaat Siddiqi
Software Developer (Senior)
United States United States
Muhammad Shujaat Siddiqi
New Jersey, USA

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Comments and Discussions

 
GeneralMy Vote of 5 Pin
Mrinal Nath TCS28-Feb-12 23:24
memberMrinal Nath TCS28-Feb-12 23:24 
GeneralMy vote of 5 Pin
jugalpanchal4-Jul-11 2:47
memberjugalpanchal4-Jul-11 2:47 
GeneralThis article helped a lot Pin
Member 224525415-Apr-10 17:16
memberMember 224525415-Apr-10 17:16 
GeneralMy vote of 1 Pin
disore7-Apr-10 20:12
memberdisore7-Apr-10 20:12 
GeneralMy vote of 1 Pin
ArchAngel1236-Apr-10 5:56
memberArchAngel1236-Apr-10 5:56 
GeneralYou haven't actually explained much about MEF here. Pin
Pete O'Hanlon3-Apr-10 9:21
mvpPete O'Hanlon3-Apr-10 9:21 
GeneralRe: You haven't actually explained much about MEF here. Pin
Davide Vitelaru3-Apr-10 21:28
memberDavide Vitelaru3-Apr-10 21:28 
Generalnteresting and Informative Pin
Makooali3-Apr-10 8:06
memberMakooali3-Apr-10 8:06 
GeneralRe: nteresting and Informative Pin
Richard Osafo7-Apr-10 11:56
memberRichard Osafo7-Apr-10 11:56 

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