I am using VS 2008 and Expression Blend 3 on a Windows 7 machine. When editing the XAML in VS8 the Split View Bar is missing. I cannot swap views nor can collapse the code or preview panes.

OK worked it out, so microsoft has done it on purpose. 

@kperwaiz

I assume you are using the Silverlight 3 Tools for Visual Studio 2008. If so, the behavior you are seeing is intentional as you've noted - the split view and visual preview pane is disabled by default for Silverlight projects in the Silverlight 3 tools release, and you will only see the XAML editor for those projects.

Blend 3 has a full designer for Silverlight 3 projects, and the next beta release of Visual Studio 2010 will also have a full designer (not just a preview pane) for Silverlight 3 projects. You can sign up to be notified when the next Visual Studio 2010 beta ships at this site:
http://www.microsoft.com/visualstudio/en-us/products/2010/default.mspx

Thanks

Mark

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Mark Wilson-Thomas - Program Team - WPF & SL Designer for Visual Studio - posts are provided 'as-is'