Class Application

   ' Application-level events, such as Startup, Exit, and DispatcherUnhandledException
   ' can be handled in this file.

   Public Property ThemeDictionary As ResourceDictionary
      ' You could probably get it via its name with some query logic as well.
      Get
         Return Resources.MergedDictionaries(0)
      End Get
      Set(value As ResourceDictionary)
      End Set
   End Property

   Public Sub ChangeTheme(uri As Uri)
      ThemeDictionary.MergedDictionaries.RemoveAt(0) ' Clear()
      Dim rd As ResourceDictionary = New ResourceDictionary()
      rd.Source = uri
      ThemeDictionary.MergedDictionaries.Add(rd) ' New ResourceDictionary()) ' Source:=uri))
   End Sub

End Class