I would suggest that you take a look at the following Code Library project:
How to Create Advanced EditAppointmentDIalog
It demonstrates how you could create a custom ViewModel for the dialog - in it you can handle the command for opening the window. Setting a DataContext to that Window will allow you to get the updated values.
I hope this will help get started with the implementation. If you have any further questions, write to us again.
Check out Telerik Analytics, the service which allows developers to discover app usage patterns, analyze user data, log exceptions, solve problems and profile application performance at run time. Watch the videos
and start improving your app based on facts, not hunches.