NotificationCenter issue on Swift 3

Question

I'm learning Swift 3 and I'm trying to using `NSNotificationCenter`. Here is my code: ``` func savePost(){ let postData = NSKeyedArchiver.archivedData(withRootObject: _loadedpost) UserDefaults.standard().object(forKey: KEY_POST) } func loadPost(){ if let postData = UserDefaults.standard().object(forKey: KEY_POST) as? NSData{ if let postArray = NSKeyedUnarchiver.unarchiveObject(with: postData as Data) as? [Post]{ _loadedpost = postArray } } //codeerror NotificationCenter.default().post(NSNotification(name: "loadedPost" as NSNotification.Name, object: nil) as Notification) } ``` and this is the observer: ``` override func viewDidLoad() { super.viewDidLoad() //codeerorr NotificationCenter.default().addObserver(self, selector: Selector(("onPostLoaded")), name: "loadedPost", object: nil) } func numberOfSections(in tableView: UITableView) -> Int { return 1 } ``` It always gives me the error "signal SIGBRT". When I try to change the name in the observer, it's not an error, but obviously it d…

Accepted Answer

Swift 3 & 4

Swift 3, and now Swift 4, have replaced many "stringly-typed" APIs with `struct` "wrapper types", as is the case with NotificationCenter. Notifications are now identified by a `struct Notfication.Name` rather than by `String`. For more details see the now legacy Migrating to Swift 3 guide

Swift 2.2 usage:

```
// Define identifier
let notificationIdentifier: String = "NotificationIdentifier"

// Register to receive notification
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification(_:)), name: notificationIdentifier, object: nil)

// Post a notification
NSNotificationCenter.defaultCenter().postNotificationName(notificationIdentifier, object: nil)
```

Swift 3 & 4 usage:

```
// Define identifier
let notificationName = Notification.Name("NotificationIdentifier")

// Register to receive notification
NotificationCenter.default.addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification), name: notificationName, object: nil)

// Post notification
NotificationCenter.default.post(name: notificationName, object: nil)

// Stop listening notification
NotificationCenter.default.removeObserver(self, name: notificationName, object: nil)
```

All of the system notification types are now defined as static constants on `Notification.Name`; i.e. `.UIApplicationDidFinishLaunching`, `.UITextFieldTextDidChange`, etc.

You can extend `Notification.Name` with your own custom notifications in order to stay consistent with the system notifications:

```
// Definition:
extension Notification.Name {
    static let yourCustomNotificationName = Notification.Name("yourCustomNotificationName")
}

// Usage:
NotificationCenter.default.post(name: .yourCustomNotificationName, object: nil)
```

Swift 4.2 usage:

Same as Swift 4, except now system notifications names are part of UIApplication. So in order to stay consistent with the system notifications you can extend `UIApplication` with your own custom notifications instead of Notification.Name :

```
// Definition:
UIApplication {
    public static let yourCustomNotificationName = Notification.Name("yourCustomNotificationName")
}

// Usage:
NotificationCenter.default.post(name: UIApplication.yourCustomNotificationName, object: nil)
```

NotificationCenter issue on Swift 3

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