Windows Phone tombstoning

There are at least hundreds of articles on Windows Phone tombstoning.  A search of "Windows Phone tombstoning" generates 277K results as of 2011-12-08. For this case, it is the best to read the document of the source - MSDN.  It is a short page with clear explanations and a perfect chart.

The most confusing part of WP tombstoning is the closing event.  There are two paths of exiting a page: 1.closing the application; 2. deactivating the page. This is solely caused by the Back button. Without the hardware Back button, there would be no such thing as app closing.  If there were a Forward button, there would not be app closing too. Usually there is nothing that one has to do for closing but not for deactivating that may lead to tombstoning. In light of this, one could do exactly the same tasks for both app closing and deactivating events.  In doing so, there may be a little bit waste of resources, but it is negligible.