Question

How to know the termination of app?

I added this code in viewDidLoad

[[NSNotificationCenter defaultCenter] addObserver:self  
selector:@selector(applicationWillTerminate:) name:UIApplicationWillTerminateNotification 
object : nil];

and if the app ends, it will notify me of termination.

- (void)applicationWillTerminate:(NSNotification*) notif{
    NSLog(@"program will end");
}   

But it doesn’t work…
I terminated the app, by clicking home button and pressing home button in 2sec, followed by clicking app icon’s ‘-‘button.

I want to be notified of the termination of app.
And also intereseted in what function to be called when the app terminates.(is it viewDidLoad?)
And the termination of app by clicking the ‘-‘button is to send the app SIGKILL?

Answer 1

I terminated the app, by clicking home button and pressing home button in 2sec, followed by clicking app icon’s ‘-‘button.

If you press the home button, your app will be sent to the background. When you then kill it (by pressing the - button), it likely does not get the notification because it is not running anymore.

applicationWillTerminate is called on iOS < 4.0, when no multitasking (background) is available or when UIApplicationExitsOnSuspend is set in the info.plist file.

On iOS 4.x, when your app is sent to the background, it receives applicationWillEnterForeground:. Look at the UIApplicationDelegate Protocol Reference for more info:

You should use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.

Keep in mind that you need to do this both in applicationWillEnterForeground and applicationWillTerminate if you also support iOS < 4

Have a look also at this post from S.O.