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How-to Q&A: How Do I Work Around a Silverlight "Catastrophic Failure" Message?

Working around some of Silverlight's subtle gotchas.

Routing out a Binding Error
Q: I'm getting the message "Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))" in my Silverlight 3 application when a particular user control is loaded. I get this message when I bind to an explicit position in an array. If I bind to a property in the source I don't have a problem, and if I bind the entire array to something like a ListBox I don't have a problem.

The stack trace is:

"   at MS.Internal.XcpImports.GetClassFullName(String 
coreClassName) at System.Windows.DependencyProp-
erty.LookupAttachedCoreProperty(String propertyName)
at System.Windows.PropertyPathParser.
GetDpFromName(String name, Boolean namespaceMapping-
Available) at System.Windows.PropertyPathParser.Rea
dAttachedPropertyStepDescriptor(Boolean calledFrom-
Parser) at System.Windows.PropertyPathParser.
ReadStepDescriptor(Boolean calledFromParser) at
System.Windows.PropertyPathParser.Parse() at
System.Windows.Data.Binding..ctor(String path,
Boolean calledFromParser) at MS.Internal.Frame-
workCallbacks.CreateBindingExtension(String con-
structorArgument, IntPtr& nativeOutValue)"

Any ideas?
A: This is Silverlight's way of saying "you confused me." So, the next place to look for a hint is the call stack. The problem is apparently in the binding, so let's look at that portion of your code:

<controls:DatePicker Grid.Row="1" Grid.Column="0" 
Name="StartDate"
DisplayDate="{Binding Values(0), Converter={StaticResource ObjectToDateConverter}}"/>

The problem is an easy-to-overlook syntax mistake in the binding. Whether you're in C# or Visual Basic, the syntax for binding to a specific element of an array from XAML uses square brackets, not parentheses. It would be nice if the XAML parser gave an error, but unfortunately this appears in a string so it leaks out as a runtime exception:

<controls:DatePicker Grid.Row="1" Grid.Column="0" 
Name="StartDate"
DisplayDate="{Binding Values[0],
Converter={StaticResource ObjectToDateConverter}}"/>

Q: I want to display the version of my application in the status bar of my Silverlight 3 application. I know the AssemblyVersion attribute is set in the AssemblyInfo file, but it does not appear in the list of attributes I get from GetCustomAttributes(). How can I retrieve the assembly version information?

A: This is a little more difficult to figure out than it should be. While the rest of the AssemblyInfo attributes appear as custom attributes, the AssemblyVersion becomes part of the assembly name. In a non-Silverlight application, you can use the assembly's GetName method to return an AssemblyName object. The AssemblyName object has a Version property.

In Silverlight the assembly's GetName method cannot be called from transparent code. You can, however, access the string version of the name using the FullName property of the assembly. The AssemblyName class includes a constructor that parses a string name. Thus, you can retrieve the assembly version using the code:

      public string Version
{
get
{
var fullName = this.GetType().Assembly.
FullName;
var assemblyName = new
AssemblyName(fullName);
return assemblyName.Version.ToString();
}
}

Because this includes a parse operation and the value isn't going to change, I'd suggest retrieving the version once and caching it to maximize performance.

About the Author

Kathleen is a consultant, author, trainer and speaker. She’s been a Microsoft MVP for 10 years and is an active member of the INETA Speaker’s Bureau where she receives high marks for her talks. She wrote "Code Generation in Microsoft .NET" (Apress) and often speaks at industry conferences and local user groups around the U.S. Kathleen is the founder and principal of GenDotNet and continues to research code generation and metadata as well as leveraging new technologies springing forth in .NET 3.5. Her passion is helping programmers be smarter in how they develop and consume the range of new technologies, but at the end of the day, she’s a coder writing applications just like you. Reach her at kathleen@mvps.org.

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