I am struggling with the same thing. However, I am distracted from the "NavigationService" because, it is claimed, the log keeps a reference to an object in memory or something that I read somewhere.
I am trying to use a frame in the main window and using mvvm light to send navigation messages to the window to change the frame.
Edit: I get it.
In the main window (the code is behind, not the viewmodel) I added Messenger.Default.Register (Of NotificationMessage (Of NavMsg)) ...
Messenger.Default.Send(Of Notificationmessage (Of NavMsg))...
NavMsg, uri .
T4 /viewmodel mvvmlight, . http://dl.activeaspsoftware.net/dl.aspx?f=MvvmLightCodeTemplates.zip