iOS NSNotificationCenter to check whether the app came from background to foreground

Question

I have a situation in which i have to intialize an object everytime when it comes from background to foreground and that should be using the NSNotificationCenter not with appdelegate because iam building a static library so there wont be appdelegate with that so please help me in the same.

Answer 1

Have you tried UIApplicationWillEnterForegroundNotification?

The app also posts a UIApplicationWillEnterForegroundNotification notification shortly before calling applicationWillEnterForeground: to give interested objects a chance to respond to the transition.

Subscribe to notification:

[[NSNotificationCenter defaultCenter] addObserver:self                                          selector:@selector(yourUpdateMethodGoesHere:)                                              name:UIApplicationWillEnterForegroundNotification                                            object:nil]; 

Implement a code, that need to be called:

- (void) yourUpdateMethodGoesHere:(NSNotification *) note { // code } 

Don't forget to unsubscribe:

[[NSNotificationCenter defaultCenter] removeObserver:self]; 

Answer 2

Swift 4.2

NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification             , object: nil)