How do you create custom notifications in Swift 3?

Question

In Objective-C, a custom notification is just a plain NSString, but it\'s not obvious in the WWDC version of Swift 3 just what it should be.

Answer 1

The advantage of using enums is that we get the compiler to check that the name is correct. Reduces potential issues and makes refactoring easier.

For those who like using enums instead of quoted strings for notification names, this code does the trick:

enum MyNotification: String {
    case somethingHappened
    case somethingElseHappened
    case anotherNotification
    case oneMore
}

extension NotificationCenter {
    func add(observer: Any, selector: Selector, 
             notification: MyNotification, object: Any? = nil) {
        addObserver(observer, selector: selector, 
                    name: Notification.Name(notification.rawValue),
                    object: object)
    }
    func post(notification: MyNotification, 
              object: Any? = nil, userInfo: [AnyHashable: Any]? = nil) {
        post(name: NSNotification.Name(rawValue: notification.rawValue), 
             object: object, userInfo: userInfo)
    }
}

Then you can use it like this:

NotificationCenter.default.post(.somethingHappened)

Though unrelated to the question, the same can be done with storyboard segues, to avoid typing quoted strings:

enum StoryboardSegue: String {
    case toHere
    case toThere
    case unwindToX
}

extension UIViewController {
    func perform(segue: StoryboardSegue) {
        performSegue(withIdentifier: segue.rawValue, sender: self)
    }
}

Then, on your view controller, call it like:

perform(segue: .unwindToX)