MEF: Unable to load one or more of the requested types
I recently walked into an issue with a WPF MEF application. The issues was only occurring on my machine, and not a colleagues. On starting the WPF application thought Visual Studio 2010 the exception “Unable to load one or more of the requested types” would be thrown inside DefaultPrismServiceRegistrar.GetRequiredPrismPartsToRegister(AggregateCatalog aggregateCatalog):
private static IEnumerable<ComposablePartDefinition> GetRequiredPrismPartsToRegister(AggregateCatalog aggregateCatalog)
{
List<ComposablePartDefinition> partsToRegister = new List<ComposablePartDefinition>();
var catalogWithDefaults = GetDefaultComposablePartCatalog();
foreach (var part in catalogWithDefaults.Parts)
{
foreach (var export in part.ExportDefinitions)
{
bool exportAlreadyRegistered = false;
foreach (var registeredPart in aggregateCatalog.Parts)
{
foreach (var registeredExport in registeredPart.ExportDefinitions)
{
if (string.Compare(registeredExport.ContractName, export.ContractName, StringComparison.Ordinal) == 0)
{
exportAlreadyRegistered = true;
break;
}
}
}
if (exportAlreadyRegistered != false) continue;
if (!partsToRegister.Contains(part))
{
partsToRegister.Add(part);
}
}
}
return partsToRegister;
}
It transpires that one of the application modules had referenced WPFToolkit.VisualStudio.Design which I assume is only for the Visual Studio design surface. Solution, remove the assembly reference.
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I’m sure it wasn’t your intention, but you have just educated me that MEF is something you can use in WPF. I thought it was a Silverlight framework.
This is a handy tool for to find out what imports are not being matched http://msdn.microsoft.com/en-us/library/ff576068.aspx in an application.