Updating the UI from child frame content to the main page content

I have a sample app here I could use a hand with :) (Thanks to Devdigital for answering the first part of my question!)

Basically I'm trying to update the TextBlock on the main page using MVVM when the content the frame updates the the property. Please find the开发者_JAVA百科 code attached below:

http://dl.dropbox.com/u/4086656/SampleApp.zip

How do i get the button inside the frame to change the variable and update the TextBlock on the parent control?

Using an Public Event and event listeners will do the trick....