如果需要用到Themes/Generic.xaml作为默认风格资源文件，不要忘了该项目的AssemblyInfo.cs中必须要有以下这段：
[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) )]
否则，程序将自动取当前操作系统风格。
这段没有的原因很可能是WPF项目是从别处拷来而不是直接在vs里创建的。
原文：http://www.cnblogs.com/dfun/p/4298290.html