07 March 2011
UPDATE: … and it wasn’t long before Matthew McDermott went ahead and implemented ths as an actual sample, which you can get here.
A while back I blogged a workaroundfor accessing some ASMX services from Silverlight 4. The problem was that the guid and char types that those services return are not recognized by Silverlight and you end up with the exception below. One of the important services affected by this is SharePoint’s UserProfileService, which I realize is pretty important to a lot of developers.
System.ServiceModel.Dispatcher.NetDispatcherFaultException was unhandled by user code. The formatter threw an exception while trying to deserialize the message: There was an error while trying to deserialize parameter http://tempuri.org/:HelloWorldResponse. The InnerException message was 'Error in line 1 position 268. Element 'http://tempuri.org/:HelloWorldResult' contains data of the 'http://microsoft.com/wsdl/types/:guid' data contract. The deserializer has no knowledge of any type that maps to this contract. Add the type corresponding to 'guid' to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding it to the list of known types passed to DataContractSerializer.'. Please see InnerException for more details.
(Same goes for http://microsoft.com/wsdl/types/:char)
We have already fixed this issue and you will not need the workaround anymore in the next version of Silverlight.
In implementing the workaround, I used an IClientMessageInspector, which unfortunately is only available starting in Silverlight 4. So all of our developers using Silverlight 3 (and in particular folks writing apps for Windows Phone 7) cannot use the workaround.
Fortunately, there is a way to “fake” an IClientMessageInspector on older versions of Silverlight, and I wrote a sample for that back in the Silverlight 2 days. So combining these two samples together, you can be on your way:
Hopefully this will unblock folks out there, if there is significant interest here I can create a combined sample that shows the whole thing end-to-end.