Why won't VisualStateManager work?

16 Feb 2009 by Nigel Sampson

As someone who's still learning Silverlight I like to put together the xaml for all my examples and experiments by hand. Since xaml and the underlying object structure for a control are exactly the same once you can compose something in xaml you can do the same in C#.

One problem with hand composing all the xaml is that I'm not as smart as software like Blend and often make mistakes. Most of the time the exception details make it pretty easy to diagnose where I'm going wrong. However while writing the previous post about using the visual state manager to style the focus panel I encountered a nasty looking exception when I call VisualStateManager.GoToState.

Error: Unhandled Error in Silverlight 2 Application Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED)) at System.Windows.VisualState.EnsureStoryboards()

The rest of the stack trace isn't important suffice to say the internal exception details proved no help. The problem is that the storyboard for that state is suffering a xaml parse issue but doesn't tell you what.

So how to diagnose? After half an hour of trying random things (bad practise I know) with no luck I found a much easier way to locate my issue. I simply created a new user control, extracted the style template and the storyboard. Bingo! 5 seconds later a nice exception telling me I had missed a "#" on one of the colour codes.

So much easier! Hope this helps someone.