Foreground 이벤트 받기

override func viewDidLoad() {
    super.viewDidLoad()
    
    NotificationCenter.default.addObserver(self, selector: #selector(onWillEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
	...
}

@objc func onWillEnterForeground() {
    if self.viewIfLoaded?.window != nil {
        // TODO : 
    }
}