title: Saving NSTimer to NSUserDefaults
body: <p>I'm doing a simple game for the iPhone and now that is finished, I'd like to add a timer. I managed to implement the timer, but now I want to pause it when an incoming SMS or Phone Call minimize the application.
  I thought that I should put the timer in the app delegate and, when applicationWillResignActive/applicationDidBecomeActive will be called, save/restore the timer object with NSUserDefaults, but I see that I can only save "raw" data, not entire objects.
  How can i manage this trouble?</p>