From Forum Nokia Wiki

ID	TSS000756	Creation date	September 27, 2007
Platform	S60 3rd Edition	Devices
Category	Base & System	Subcategory	Application Framework

Keywords (APIs, classes, methods, functions):

Overview

Applications may require to do some operations, such as saving data, when being closed without the user's intervention. An application may be closed due to sudden shutdown of the device, either caused by low memory, powering off, or low battery.

Description

This can be handled by checking for the EApaSystemEventShutdown which is sent to all running applications.

Solution

In GUI applications you can check for the event in the HandleSystemEventL method of the UI.

 void CTestAppUi::HandleSystemEventL(const TWsEvent& aEvent)
   {
   switch (*(TApaSystemEvent*)(aEvent.EventData()))
     {
     case EApaSystemEventShutdown:
       // do things here
       break;
     default:
       break;
     }
   // call base class implementation
   CAknAppUi::HandleSystemEventL(aEvent);
   }

This event can also be received in background applications that do not use the application framework, by requesting notifications directly from the window server. In a CActive-derived class, this can be done as follows:

 // During construction
 // Create a session to window server
 // iWs is a class member of type RWsSession
 User::LeaveIfError(iWs.Connect()); 
 
 ...
 
 // listen for WSERV events
 iWs.EventReady(&iStatus);
 SetActive();
 

And in the implementation of CActive::RunL():

 if (iStatus.Int() == KErrNone)
   {
   TWsEvent event;
   iWs.GetEvent(event);
   switch(*(TApaSystemEvent*)(event.EventData()))
     {
     case EApaSystemEventShutdown:
       {
       // do things here
       break;
       }
     default:
       break;
     }
   // issue a new request
   iWs.EventReady(&iStatus);
   SetActive();
   }
 

Also remember to call RWsSession::EventReadyCancel() in CActive::DoCancel(), and RWsSession::Close() in the destructor.