After calling IContentLibraryContext.GetItem() and IContentLibraryListItem.Id for a Multimedia item (EclItemTypes.File) the Tridion CME throws the following error. The exception does not show up in Visual Studio while attaced to the TcmServiceHost process so I think something in the Tridion ECL ran into something unexpected.

I have compared the code against the Flickr example implementation but cannot find what I would do wrong. Any ideas why this error would pop up?

Unable to cast object of type Tridion.ExternalContentLibrary.AddInPipeline.V2.HostSideAdapters.ContentLibraryItemContractToViewHostAdapter' to type 'Tridion.ExternalContentLibrary.AddInPipeline.V2.HostViews.IContentLibraryMultimediaItem'.

Error detail:

StackTrace Information Details: at Tridion.ExternalContentLibrary.DomainModel.ItemDataBuilder.ToFullItemData(IContentLibraryItem item, String stubSchemaId, StubItemListData stubItemListData, IDictionary2 displayTypes) at Tridion.ExternalContentLibrary.DomainModel.FileItemDataBuilder.BuildResultListItemData() at Tridion.ExternalContentLibrary.Service.EclService2012.GetFile(EclUri eclUri, Func3 getStubId, Action1 stubItemManipulations, Nullable1 openMode) at Tridion.ExternalContentLibrary.Service.EclService2012.GetItem(String itemUri, Int32 openMode) at SyncInvokeGetItem(Object , Object[] , Object[] ) at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs) at Tridion.ExternalContentLibrary.Service.TransactionSupportInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs) at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc& rpc) at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)

1 Answer 1


For an item of the File type, make sure you return an instance of IContentLibraryMultimediaItem from GetItem and GetItems.

The exceptions can be a bit hard to read, as they originate from the code connecting the different versions of the contracts.

  • That's it! I implemented IContentLibraryItem instead of IContentLibraryMultimediaItem. The IContentLibraryMultimediaItem implements IContentLibraryItem which implements IContentLibraryListItem, that helps creating a clean implementation of all those items without having to duplicate a lot of code for getting parent ids and so on.
    – Jan H
    Commented Oct 16, 2013 at 11:52
  • 1
    Yes, but then I'll have higher ranking than he does :) Commented Oct 16, 2013 at 13:56
  • Lars, you already have a higher reputation.
    – Jan H
    Commented Oct 16, 2013 at 16:27

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