Windows phone 7 silverlight tombstoning

I have read in requirements that when user presses the back button, application must exit. (5.4.2): "Pressing the Ba开发者_Python百科ck button from the first screen of an application must exit the application".

So, i have read in many sites that exitting in silverlight is not available, but i think that they mean, that application should only deactivate (for example, it is deactivated when we press button with "windows flag"). I have a main menu in my application. If i navigate on another pages and return to main menu, pressing "back button" doesn't deactivate application because previous pages are another pages in application. So, maybe I need to clean "navigation history" ? But it is not possible, i have readed it somewhere... so, what to do in this case?

The back button must exit the application from the first screen in your application. Your application is supposed to navigate backwards through your page stack if the user has navigated forwards through your pages.

This requirement simply means that you application must not prevent the user from exiting the application when the press the back button and have reached the first page.

First off, there is no explicite exiting in Silverlight. There is no Exit() method.
Think of your app as a webapp and whole navigation system is like a simple browser with back, home and search button.

Can you close stackoverflow.com ? you can back to another site (if any) or press start/home button to leave stackoverflow (if it's not your home page :) )

In Windows Phone 7 the behaviour you describe as "deactivate" is called Tombstoning.

You can use Non-linear Navigation Service to solve your problem with navigation.