WPF - Resource not loading from Generic.xaml - wpf

Question

Themes\Generic.xaml:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="WPF Commons;component/Controls/Layout/Foo/FooItem.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
Controls\Layout\Foo\FooItem.xaml:
<Style TargetType="{x:Type l:FooItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type l:FooItem}">
<Border>
<ContentPresenter ContentSource="Header" />
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
If I copy the entire style into my usercontrol resources it works fine. But, if I don't, the usercontrol shows up empty. In Expression Blend 4, I right-clicked and chose Edit Template>, but it won't let me select Edit a Copy... which leads me to believe that something is severely wrong and the Generic.xaml isn't loading properly. I figure it's Generic.xaml because if I remove the MergedDictionary call and copy/paste the xaml style directly into Generic.xaml it still doesn't work.

Answer 1

I'm gonna take a wild guess that you altered your AssemblyInfo.cs file and either changed (or removed) the following line:
[assembly: ThemeInfo(
ResourceDictionaryLocation.None, //where theme specific resource dictionaries are located
//(used if a resource is not found in the page,
// or application resource dictionaries)
ResourceDictionaryLocation.SourceAssembly //where the generic resource dictionary is located
//(used if a resource is not found in the page,
// app, or any theme specific resource dictionaries)
)]
You need to tell your assembly about your ThemeInfo. :)

Answer 2

copying from my blog: http://zoomicon.wordpress.com/2012/06/10/what-to-do-if-generic-xaml-doesnt-get-loaded-for-wpf-control/
at the start of Properties\AssemblyInfo.cs you need (note this isn’t used/needed in Silverlight):
using System.Windows;
...
Mind you that if the project doesn’t show a Properties node in Solution Explorer, you have to either make a new project using the correct template (for a WPF custom control), or right click the project, select Properties, then press the Assembly Information button and enter some dummy values, then OK to create the Properties node (which also creates to a Properties subfolder and AssemblyInfo.cs file).
You can expand (drop-down) the special Properties node in solution explorer then to open AssemblyInfo.cs and add the above stuff if missing