New Post: Resolving Open Generics with RegistrationBuilder

Hi Kathleen,

Here is a response from Kevin on the MEF team.

Yes it is possible to export generics using RegistrationBuilder.

There is a bug in Desktop MEF that we didn’t fix. We did fix it in Oob MEF.

The work around is to use code like this, the bold is what she needs to add the rest is to make it a complete sample:

using System;

using System.Collections.Generic;

using System.ComponentModel.Composition;

using System.ComponentModel.Composition.Hosting;

using System.ComponentModel.Composition.Registration;

using System.Linq;

using System.Reflection;

using System.Text;

using System.Threading.Tasks;

namespace ConsoleApplication26

{

publicinterfaceIRepository<T>

{

IEnumerable<T> GetItems();

}

publicclassExampleRepository<T> :IRepository<T>where T :class

{

publicIEnumerable<T> GetItems()

{

returnnewList<T>();

}

}

[Export]

publicclassImporter

{

[ImportMany]

publicIEnumerable<string> Items;

}

classProgram

{

privatestaticbool IsGenericDescendentOf(TypeInfo openType, TypeInfo baseType)

{

if (openType.BaseType == null)

{

returnfalse;

}

if (openType.BaseType == baseType.AsType())

{

returntrue;

}

foreach (Type typein openType.ImplementedInterfaces)

{

if (type.IsConstructedGenericType && (type.GetGenericTypeDefinition() == baseType.AsType()))

{

returntrue;

}

}

return IsGenericDescendentOf(IntrospectionExtensions.GetTypeInfo(openType.BaseType), baseType);

}

privatestaticbool IsDescendentOf(Type type, Type baseType)

{

if (((type == baseType) || (type == typeof(object))) || (type == null))

{

returnfalse;

}

TypeInfo typeInfo = IntrospectionExtensions.GetTypeInfo(type);

TypeInfo info2 = IntrospectionExtensions.GetTypeInfo(baseType);

if (typeInfo.IsGenericTypeDefinition)

{

return IsGenericDescendentOf(typeInfo, info2);

}

return info2.IsAssignableFrom(typeInfo);

}

staticvoid Main(string[] args)

{

var reg = newRegistrationBuilder();

reg.ForTypesMatching((t) =>

{

return IsDescendentOf(t, typeof(IRepository<>));

}).Export((eb) => eb.AsContractType(typeof(IRepository<>)));

var cat = newTypeCatalog(newType[] {typeof(ExampleRepository<>),typeof(Importer) }, reg );

var container = newCompositionContainer(cat);

var importer = container.GetExportedValue<Importer>();

if (importer.Items == null)

{

Console.WriteLine("Failed");

}

}

}

}

hth

cheers

-alok

From: KathleenDollard