viewWillAppear 동작 context

viewWillAppear는 foreground에서 실행 중인 app에 대해 동작한다. 다른 앱에 갔다가 다시 돌아와서 foreground 로 보일때는 동작하지 않음. 따라서 UIApplication.willEnterForegroundNotification 등록 필요

override func viewDidLoad() {
  super.viewDidLoad()

  // set observer for UIApplication.willEnterForegroundNotification
  NotificationCenter.default.addObserver(self, 
                                         selector: #selector(willEnterForeground), 
                                         name: UIApplication.willEnterForegroundNotification, 
                                         object: nil)
}

@objc func willEnterForeground() {
}

deinit {
  NotificationCenter.default.removeObserver(self,
                                            name: UIApplication.willEnterForegroundNotification, 
                                            object: nil)
}

출처

Why does viewWillAppear not get called when an app comes back from the background?

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