Expression Blend Error - The value cannot be null. Parameter Name: Stream

Question

I get the above error when trying to load the User Control xaml file in the design view in Expression Blend 4. xaml itself starts up successfully in VS 2010, and I can view the xaml in blend, but not in the design. When viewing xaml in the xaml view, the UserControl underlined in red. Anyone facing this problem?

Answer 1

You must remember that in order to render the control, the developer will have to execute part of his code. If the code that it runs does things (such as WCF calls) that the design context does not support, you may have problems.

For this reason, the Silverlight API contains a class DesignerPropertiesin the namespace System.ComponentModel. Use its static property IsInDesignToolto skip / mock code that runs while loading a control that is not supported in the designer.