application is already running the dispatcher
Typically, in an MVVM Light application, the DispatcherHelper is initialized in App.xaml.cs, which is the file defining the startup class of the application. In Windows Phone, you call DispatcherÂ­Helper.Initialize in the InitializePhoneApplication method, right after the applicationâs main frame is created.
The code above in bold accomplishes the task of shutting down the dispatcher for windowâs UI thread. Running multiple UI threads in WPF application is actually rather trivial. In the nutshell it boils down to creating your dedicated thread and creating your windows inside this threadâs proc. Remember to conclude your UI thread with a call to WPF dispatcher.