Currently the Managed Extensibility Framework (MEF) does not have documentation/steps for creating a new WPF Application (there is documentation for a console application) so I figured I'd document the steps I take here; there are plenty of samples to get me going.

1. Create New WPF Application
2. Remove the StartupUri="Window1.xaml" from the App.xaml file
3. Add a reference to the Projects | ComponentModel project
4. Add the following code to the App.xaml.cs code-behind file:
   
   
       /// <summary>
       /// Interaction logic for App.xaml
       /// </summary>
       public partial class App : Application
       {
           private CompositionContainer _container;
   
           [Import("MainWindow")]
           public new Window MainWindow
           {
               get { return base.MainWindow; }
               set { base.MainWindow = value; }
           }
   
           protected override void OnStartup(StartupEventArgs e)
           {
               base.OnStartup(e);
   
               if (Compose())
               {
                   MainWindow.Show();
               }
               else
               {
                   Shutdown();
               }
           }
           protected override void OnExit(ExitEventArgs e)
           {
               base.OnExit(e);
   
               if (_container != null)
               {
                   _container.Dispose();
               }
           }
           private bool Compose()
           {
               var catalog = new AggregatingComposablePartCatalog();
               catalog.Catalogs.Add(new AttributedAssemblyPartCatalog(Assembly.GetExecutingAssembly()));
   
               _container = new CompositionContainer(catalog.CreateResolver());
               _container.AddPart(this);
   
               try
               {
                   _container.Compose();
               }
               catch (CompositionException compositionException)
               {
                   MessageBox.Show(compositionException.ToString());
                   return false;
               }
               return true;
           }
   
       }
    
   
   
5. Add an [Export("MainWindow")] attribute to the Window1.xaml.cs file's Window1 class.
   
   
   
   
6. Compile and run the application - your Window1.xaml file should load.  If you get two windows then you failed to comply with step #2 above

A less conventional route is to use a "BootStrapper" class

The BootStrapper code follows:

namespace MEFContrib.Library.Base
{
    public class BootStrapper
    {
        private Assembly _assembly;
        private Application _application;
        private CompositionContainer _container;

        public BootStrapper(object sender, BootStrapperEventArgs e)
        {
            _application = sender as Application;
            _assembly = e.Assembly;

            _application.Exit += new ExitEventHandler(_application_Exit);

            if (Compose())
                _application.MainWindow.Show();
            else
                _application.Shutdown();
        }

        void _application_Exit(object sender, ExitEventArgs e)
        {
            if (_container != null)
                _container.Dispose();
        }

        private bool Compose()
        {
            var catalog = new AggregatingComposablePartCatalog();
            catalog.Catalogs.Add(new AttributedAssemblyPartCatalog(_assembly));
            ((IMefApplication)_application).OnAddCatalog(catalog.Catalogs);

            _container = new CompositionContainer(catalog.CreateResolver());
            _container.AddPart(_application);

            try
            {
                _container.Compose();
            }
            catch (CompositionException compositionException)
            {
                MessageBox.Show(compositionException.ToString());
                return false;
            }
            return true;
        }
    }
}

MEF_QuickStart.zip (2.10 mb)