36

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.

user3115014
  • 667
  • 1
  • 8
  • 23

7 Answers7

46

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];
Nikita Took
  • 3,980
  • 25
  • 33
  • Check this one: http://stackoverflow.com/questions/2191594/send-and-receive-messages-through-nsnotificationcenter-in-objective-c – Vinod Singh Jul 23 '14 at 12:53
28

Swift 4.2

NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification
            , object: nil)
Community
  • 1
  • 1
Andrea Miotto
  • 7,084
  • 8
  • 45
  • 70
16

Swift 5

Subscribe to Notification -

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

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

Remove subscription - 

override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)

        NotificationCenter.default.removeObserver(self)
}

Function to be called - 

@objc func applicationWillEnterForeground(_ notification: NSNotification) {
       self.volumeSlider.value = AVAudioSession.sharedInstance().outputVolume
    }
Kiran Jasvanee
  • 6,362
  • 1
  • 36
  • 52
12

Swift 3 version

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    NotificationCenter.default.addObserver(self,
                                           selector:#selector(applicationWillEnterForeground(_:)),
                                           name:NSNotification.Name.UIApplicationWillEnterForeground,
                                           object: nil)
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    NotificationCenter.default.removeObserver(self)
}

func applicationWillEnterForeground(_ notification: NSNotification) {
   ....
}

you can also use NSNotification.Name.UIApplicationDidBecomeActive

mt81
  • 3,288
  • 1
  • 26
  • 35
4

Swift 5 use: UIApplication.willEnterForegroundNotification

SmileBot
  • 19,393
  • 7
  • 65
  • 62
3

swift 5

 override func viewDidAppear(_ animated: Bool) {
    NotificationCenter.default.addObserver(self, selector: #selector(appMovedToForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
    }
    
    override func viewDidDisappear(_ animated: Bool) {
    NotificationCenter.default.removeObserver(self, name: NSNotification.Name(rawValue: UIApplication.willEnterForegroundNotification.rawValue), object: nil)
    }

    @objc func appMovedToForeground() {
       // Do stuff
   }
Gurjinder Singh
  • 9,221
  • 1
  • 66
  • 58
2

Swift 3 and 4 version

NotificationCenter.default.addObserver(forName: NSNotification.Name.UIApplicationWillEnterForeground, object: nil, queue: nil) { notification in
        ...
}
omerx
  • 181
  • 1
  • 3