.NET 4.0 MEF FAQ (Socket, Plug and extension)

.NET 4.0 MEF FAQ (Socket, Plug and extension) 

• Introduction and Goal
• What is MEF (Manage extensibility framework)?
• How can we implement MEF in .NET 4.0?
• Can we see a simple example of MEF with the above 3 steps?
• Should data types of import and export match?
• Can we connect import and export via some defined contract rather than .NET data types?
• This looks very much similar like DI and IOC, why the re-invention?
• Can they work hand on hand?
• We would like to see a sample in Silverlight?
• Can we also see a simple Sample in WPF?
• How about some Sample in ASP.NET?
• Source code
• Reference
  

Introduction and Goal

What is MEF (Manage extensibility framework)?

How can we implement MEF in .NET 4.0?

• Import (Create the socket) - Use the "Import" attribute to define a hook or socket in your application.
• Export (Attach the Plug) - Use the "Export" attribute to create the plug which can attach to the plug or hook.
• Compose (Extend it) - Use the composition container and compose it.
  

Can we see a simple example of MEF with the above 3 steps?

using System.ComponentModel.Composition;
using System.ComponentModel.Composition.Hosting;
using System.Reflection;

class Program
{
[Import()]
public string ImportMessage
{
set;
get;
}
}

class clsMySimpleMessage
{
[Export()]
string ExportMessage
{
set
{
}
get
{
return "Message inserted via MEF";
}
}

}

private void Compose()
{
// Get a reference to the current assemblies in the project.
AssemblyCatalog catalog = new AssemblyCatalog(Assembly.GetExecutingAssembly());

// Once you have got the reference of catalog add it to the composition container.
CompositionContainer compositionContainer = new CompositionContainer(catalog);

// Finally call composeparts to connect the Import with Export.
compositionContainer.ComposeParts(this);

// use the property
Console.WriteLine(ImportMessage);
Console.ReadLine();
}

Should data types of import and export match?

Can we connect import and export via some defined contract rather than .NET data types?

interface ImyInterface
{
string getString();
}

[Export(typeof(ImyInterface))]
class clsMyImplementation : ImyInterface
{
public string getString()
{
return "This is my string";
}
}

class Program
{
[Import()]
public ImyInterface myInterface
{
set;
get;
}
}

This looks very much similar like DI and IOC, why the re-invention?

Can they work hand on hand?

We would like to see a sample in Silverlight?

public partial class MainPage : UserControl
{
[ImportMany]
public ObservableCollection<UserControl> ImportedItems
{ get; set; } 
}

[Export(typeof(UserControl))]
public partial class SilverlightControl1 : UserControl
{
public SilverlightControl1()
{
InitializeComponent();
}
}


[Export(typeof(UserControl))]
public partial class SilverlightControl2 : UserControl
{
public SilverlightControl2()
{
InitializeComponent();
}
}

CompositionInitializer.SatisfyImports(this);

Can we also see a simple Sample in WPF?
 

How about some Sample in ASP.NET?
 

Source code

Reference

• Hansel and Glenn talks about difference between MEF and IOC on http://www.hanselminutes.com/default.aspx?showID=166 
• 10 reasons why to use MEF
• http://csharperimage.jeremylikness.com/2010/04/ten-reasons-to-use-managed.html 
• MEF for beginners
• http://blogs.microsoft.co.il/blogs/bnaya/archive/2009/11/28/mef-for-beginner-concept-part-1.aspx 
• As said by Sreeni Ramadurai its import, export and bind
• http://mstecharchitect.blogspot.com/2010/02/mef-managed-extensibility-framework.html
• Simple article on MEF
• http://www.sidarok.com/web/blog/content/2008/09/26/what-is-this-managed-extensibility-framework-thing-all-about.html