VS2010/Silverlight designer unhandled exception

Question

I have VS2010 10.0.30319.1 RTMRel and Silverlight 4 installed.

Let me make it clear that I've worked on several projects without any designer issue.

I don't recall messing with either VS or Silverlight 4, however today when I opened a project and tried to tweak the UI of my web application, the designer wouldn't load. I created a new project, and the same thing happed. Below is the exception. Any help will be appreciated.

System.NullReferenceException
Object reference not set to an instance of an object.
   at Microsoft.Windows.Design.Platform.SilverlightMetadataContext.SilverlightXamlExtensionImplementations.<GetXmlNamespaceCompatibilityMappings>d__8.MoveNext()
   at MS.Internal.Design.Metadata.ReflectionProjectNode.BuildSubsumption()
   at MS.Internal.Design.Metadata.ReflectionProjectNode.SubsumingNamespace(Identifier identifier)
   at MS.Internal.Design.Markup.XmlElement.BuildScope(PrefixScope parentScope, IParseContext context)
   at MS.Internal.Design.Markup.XmlElement.ConvertToXaml(XamlElement parent, PrefixScope parentScope, IParseContext context, IMarkupSourceProvider provider)
   at MS.Internal.Design.DocumentModel.DocumentTrees.Markup.XamlSourceDocument.FullParse(Boolean convertToXamlWithErrors)
   at MS.Internal.Design.DocumentModel.DocumentTrees.Markup.XamlSourceDocument.get_RootItem()
   at Microsoft.Windows.Design.DocumentModel.Trees.ModifiableDocumentTree.get_ModifiableRootItem()
   at Microsoft.Windows.Design.DocumentModel.MarkupDocumentManagerBase.get_LoadState()
   at MS.Internal.Host.PersistenceSubsystem.Load()
   at MS.Internal.Host.Designer.Load()
   at MS.Internal.Designer.VSDesigner.Load()
   at MS.Internal.Designer.VSIsolatedDesigner.VSIsolatedView.Load()
   at MS.Internal.Designer.VSIsolatedDesigner.VSIsolatedDesignerFactory.Load(IsolatedView view)
   at MS.Internal.Host.Isolation.IsolatedDesigner.BootstrapProxy.LoadDesigner(IsolatedDesignerFactory factory, IsolatedView view)
   at MS.Internal.Host.Isolation.IsolatedDesigner.BootstrapProxy.LoadDesigner(IsolatedDesignerFactory factory, IsolatedView view)
   at MS.Internal.Host.Isolation.IsolatedDesigner.Load()
   at MS.Internal.Designer.DesignerPane.LoadDesignerView()

Martin Randall Martin Randall · Accepted Answer · 2012-10-26T08:46:16

When this happens to me, it means that I have broken something in the code. The designer is essentially running your Silverlight code in order to generate a preview - so that would be the first thing to investigate.

Secondly - is this happening when you look at any piece of Silverlight Xaml? If create a new Silverlight project, do you stil get the same issue. If that is the case, then you've messed up your installation somehow.

I've spent many happy hours with Silverlight 5 and the VS2010 designer, so I don't think there is a fundamental issue there.

VS2010/Silverlight designer unhandled exception

1 Answers