Question

I am trying to dynamically (using reflection) add types to a MEF catalog and also define the export contract at runtime. The issue is MEF will simply use the fully qualified name of the type as the contract, and I need to specify the export contract as a specific interface type.

Here is the code I use to get the types I need to add to the MEF catalog:

private void RegisterSupportedRepositories(Func<ObjectContext> contextProvider)
    {
        var context = contextProvider();
        var properties = context.GetType().GetProperties();
        var entitySets = properties.Where(property => property.PropertyType.Name == typeof(ObjectSet<>).Name);

        foreach (var entitySet in entitySets)
        {
            var entityType = entitySet.PropertyType.GetGenericArguments()[0];
            var repositoryType = typeof(EFRepository<>).MakeGenericType(entityType);
            ComponentServices.RegisterComponent(repositoryType);                
        }
    }

ComponentServices.RegisterComponent is defined below, it gets an AggregateCatalog (from where isn’t relevant) and then adds TypeCatalogs to the aggregate catalog:

public static void RegisterComponent(Type componentType)
    {
        var catalog = RetrieveCatalog();

        catalog.Catalogs.Add(new TypeCatalog(componentType));
    }

I need to be able to specify the contract of the added types as an interface, this would normally be done with Export attributes that look like this:

[Export(typeof(IRepository<Customer>))]

The question is how do I add this export contract dynamically, so that the export is equivalent to what’s shown above and not the default “EFRepository” contract that MEF infers from the type itself.

Answer 1

If you can use the CodePlex preview version of MEF, I’d recommend using the new RegistrationBuilder to do this. Here’s a blog post describing it: MEF’s Convention Model

If you can’t use the preview version, you can use the methods in ReflectionModelServices to create your own part definitions, and create a catalog implementation that uses them.