The nice thing about MEF is the ability to dynamically load additional modules in to an application with very little effort.

To make it even easier, I’ve generated a small MEF Compose which will load up all DLL in a directory automatically.

private void Compose()
        {
            var catalog = new AggregateCatalog(
                new AssemblyCatalog(System.Reflection.Assembly.GetExecutingAssembly()),
                new DirectoryCatalog(@”.\Extensions”));
            var container = new CompositionContainer(catalog);
            container.ComposeParts(this);
        }

The above code works well for .NET, however for some reason .NET 3.5 version, which is available from CodePlex just comes back with nulls, so here is a solution for MEF for .NET 3.5

private void Compose()
        {
            var key = Assembly.GetExecutingAssembly().GetName().GetPublicKey();
            var catalog = new AggregateCatalog();
            catalog.Catalogs.Add(new AssemblyCatalog(Assembly.GetExecutingAssembly()));
            var dir = new DirectoryInfo(@”.\Extensions”);
            Assembly assembly;

            foreach (var file in dir.GetFiles(“*.dll”))
            {
                assembly = Assembly.LoadFile(file.FullName);
                byte[] assemblykey = assembly.GetName().GetPublicKey();
                catalog.Catalogs.Add(new AssemblyCatalog(assembly));
            }

            var container = new CompositionContainer(catalog);
            container.ComposeParts(this);
        }