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

You can add a custom initializer to NSNotification.Name

extension NSNotification.Name {
    enum Notifications: String {
        case foo, bar
    }
    init(_ value: Notifications) {
        self = NSNotification.Name(value.rawValue)
    }
}

Usage:

NotificationCenter.default.post(name: Notification.Name(.foo), object: nil)

Answer 2

if you use string-only custom notifications, there's no reason to extend any classes but String

    extension String {
        var notificationName : Notification.Name{
            return Notification.Name.init(self)
        }
    }

Answer 3

I may suggest another option which is similar to what @CesarVarela suggested.

extension Notification.Name {
    static var notificationName: Notification.Name {
        return .init("notificationName")
    }
}

This will let you post and subscribe on notifications easily.

NotificationCenter.default.post(Notification(name: .notificationName))

Hope this will help you.

Answer 4

NSNotification.Name(rawValue: "myNotificationName")

Answer 5

You could also use a protocol for this

protocol NotificationName {
    var name: Notification.Name { get }
}

extension RawRepresentable where RawValue == String, Self: NotificationName {
    var name: Notification.Name {
        get {
            return Notification.Name(self.rawValue)
        }
    }
}

And then define your notification names as an enum anywhere you want. For example:

class MyClass {
    enum Notifications: String, NotificationName {
        case myNotification
    }
}

And use it like

NotificationCenter.default.post(name: Notifications.myNotification.name, object: nil)

This way the notification names will be decoupled from the Foundation Notification.Name. And you will only have to modify your protocol in case the implementation for Notification.Name changes.

Answer 6

There is a cleaner (I think) way to achieve it

extension Notification.Name {

    static let onSelectedSkin = Notification.Name("on-selected-skin")
}

And then you can use it like this

NotificationCenter.default.post(name: .onSelectedSkin, object: selectedSkin)