(XAML)"XXXX" does not exist in the namespace "clr-

Error 139 Assembly 'System.Activities.Core.Presentation' was not found. Verify that you are not missing an assembly reference. Also, verify that your project and all referenced assemblies have been built. EnumerationTestDesigner.xaml 6 17 LoganTests
Error 138 XXXXXXXXThe name "DesignerStylesDictionary" does not exist in the namespace "clr-namespace:System.Activities.Core.Presentation.Themes;assembly=System.Activities.Core.Presentation". 

原因很简单，工程文件中没有引用'System.Activities.Core.Presentation'