Windows Phone 7 Tombstoning

Windows Phone 7.1 Lifecycle

Windows Phone 7.1 (Mango) introduces a much more convincing illusion of multi-tasking, where the user can press and hold the back-button to rapidly switch between a small number of apparently concurrently running applications. However, again this is not true multitasking.

To achieve this, WP7.1 introduces a new state in the application lifecycle, the Dormant state:

When your application is in a Dormant state it is still in memory, however it is not executing. This allows the phone to re-start your application much more rapidly than when it is in a tombstoned state.

The phone can only store a limited number of dormant applications, as a result it might choose to move your application from a dormant to a tombstoned state. You do not receive any notification that this has occurred. However, the tombstoning and re-activiation process is the same as that for WP7.0, where you re-activate your application from the data saved in the State dictionary.

Again, there is always the possibility that your tombstoned data will be pushed out of the back-stack and lost.

Notice that there have not been any new events added to indicate that your application has returned from a Dormant state, your application will always receive Activated event when it is restarted regardless of whether it was dormant or tombstoned. This is good news, because it is backwards compatible with WP7.0.

Handling the Dormant State

So how do you handle this new state in your application? In order to maintain backwards compatibility you don’t strictly have to, however it is actually very simple to do.

The event arguments passed to the Activated event now have a new IsApplicationInstancePreservedargument which is true if your application has been re-started from a dormant state and false if it has been restarted from a tombstoned state. If this argument returns true, you simply do nothing! This ensures that you do not perform any redundant actions and helps your application restart faster.

The code below is all of the lifecycle code (apart from per-page UI state) that my MVVM example application contains. You can see that the code for a re-activated dormant state does nothing.

Extracted From - http://www.codeproject.com/Articles/269352/A-Windows-Phone-7-1-Mango-MVVM-Tombstoning-Example