Decoupled notification center subscription

decouplednotificationcentersubscription.swift

//1) Notification center-specific implementation of UpdateObserving

class NotificationObserver: UpdateObserving {
    
    var observer: NSObjectProtocol?
    
    init(notificationObserver: NSObjectProtocol?) {
        self.observer = notificationObserver
    }
    
    func unsubscribe() {
        if(observer != nil) {
            NotificationCenter.default.removeObserver(observer!)
        }
    }
}

//2) Repository method that subscribes to notifications

func observeRecordChanges(completionBlock: @escaping ([RecordModel]) -> ()) -> UpdateObserving {
        let observer = NotificationCenter.default.addObserver(forName: NSNotification.Name(rawValue: "RecordsChangedNotification"), object: nil, queue: nil) { (notification) in
            let records = //get records from somewhere
            completionBlock(records)
        }
  
  return NotificationObserver(notificationObserver: observer)
}

//3) TableViewController.swift- doesn't this look familiar?

var records = [RecordModel]()
var recordObserver: UpdateObserving?
var repository = RepositoryWithNotificationCenterBasedSubscriptions()

func viewWillAppear(_ animated: Bool) {
  self.recordObserver = self.repository.observeRecordChanges(completionBlock: { [unowned self] (records) in
      DispatchQueue.main.async { [unowned self] in
         self.records = records
         self.tableView.reloadData()
      }
}

// don't forget to clean up after yourself or things will get slow or buggy or both                                                                //
func viewWillDissappear(_ animated: Bool) {
  self.recordObserver?.unsubscribe()
}