Notifications

NotificationObserver.swift

// Jared Sinclair: https://twitter.com/jaredsinclair/status/951536021459619840

class NotificationObserver {
    private var observers = [NSObjectProtocol]()
    private let queue: OperationQueue
    
    init(queue: OperationQueue = .main) {
        self.queue = queue
    }
    
    deinit {
        observers.forEach { NotificationCenter.default.removeObserver($0) }
    }
    
    func when(_ name: Notification.Name, perform block: @escaping (Notification) -> ()) {
        let center = NotificationCenter.default
        let observer = center.addObserver(forName: name, object: nil, queue: queue, using: block)
        observers.append(observer)
    }
}

class MyViewController: UIViewController {
    private let observer = NotificationObserver()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        observer.when(.UIApplicationDidBecomeActive) { [weak self] _ in
            // Do something
        }
        observer.when(.UIApplicationDidEnterBackground) { [weak self] _ in
            // Do something (else)
        }
    }
}