Question

i really dont get it work.

say i have some classes with the same interface which i want to export.

[Export(typeof(IService))]
[ExportMetadata("ExportType", typeof(Service1))]   
public class Service1 : IService
{...}
[Export(typeof(IService))]
[ExportMetadata("ExportType", typeof(Service2))]   
public class Service2 : IService
{...}
[Export(typeof(IService))]
[ExportMetadata("ExportType", typeof(Service3))]   
public class Service3 : IService
{...}

now i have one class which import the IService and this class did not matter wich service it is.

public class Blup
{
   [ImPortingConstructor]
   public Blup(IService service)
   {}
}

what i try to achieve now is to build an ExportProvider which select the right Export on Compose.

Something like this:

public TypeExportProvider<TTypeToExport>() : ExportProvider
{}

i really have no idea how the

protected override IEnumerable<Export> GetExportsCore(ImportDefinition definition, AtomicComposition atomicComposition)

should look like. maybe anyone know a blog to read about this. there a lot of custom ExportProvider samples out but not for this situation.

thx

Answer 1

Hi Kent if you look at the exports there are metadata called “ExportType”, this should be the selector for the custom exportprovider.
but after posting here a found a blog post from glenn block. so for my special purpose i have to do is this:

var catalog = new AggregateCatalog(); 
catalog.Catalogs.Add(new DirectoryCatalog(AppDomain.CurrentDomain.BaseDirectory)); 
var defaults = new CatalogExportProvider(new TypeCatalog(typeof(Service2))); 
var container = new CompositionContainer(catalog, defaults); 
defaults.SourceProvider = container;

never the less it would be nice to see how can i write a custom exportprovider which select the right export from metadata information. my problem is how can a choose the right information from ImportDefnition and how could i set the new Export(…) in GetExportsCore().