If you need a class other than the app delegate to respond to the various application events, then have the other class register for the various application notifications.
For example, to deal with the app entering the background:
// Put this in the class that needs to deal with entering the background
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(backgrounding) name:UIApplicationDidEnterBackgroundNotification object:nil];
See the docs for UIApplication
for a list of all of the notifications.
Don't forget to remove the observer in the dealloc
method of the class.