let nc = NotificationCenter.default<\/code>. In addition the model of using selectors has changed<\/i> to specifying a block or funtion to execute when the notificaiton is received.<\/p>\nFor example, in Swift 2 we would write:<\/p>\n
\nlet nc = NSNotificationCenter.defaultCenter()\nnc.addObserver(self, \n selector: #selector(ViewController.catchNotification),\n name: \"MyNotification\", \n object: nil)\n<\/pre>\nwhereas Swift 3 code would look like this:<\/p>\n
\nlet nc = NotificationCenter.default \/\/ Note that default is now a property, not a method call\nnc.addObserver(forName:Notification.Name(rawValue:\"MyNotification\"),\n object:nil, queue:nil,\n using:catchNotification)\n<\/pre>\nIn this example we’re instructing the notification center to deliver MyNotification<\/code> notifications to the catchNotification<\/code> function which has a signature of (Notification) -> Void<\/code>. Alternatively we could use a trailing closure:<\/p>\n\nlet nc = NotificationCenter.default \/\/ Note that default is now a property, not a method call\nnc.addObserver(forName:Notification.Name(rawValue:\"MyNotification\"),\n object:nil, queue:nil) {\n notification in\n \/\/ Handle notification\n}\n<\/pre>\nPost It!<\/h3>\n
Now, let’s look at posting<\/i> (sending) a notification. The postNotificationName<\/code> method in Swift 2.0 has been replaced with post<\/code> in Swift 3.0.<\/p>\n\nlet nc = NotificationCenter.default\nnc.post(name:Notification.Name(rawValue:\"MyNotification\"),\n object: nil,\n userInfo: [\"message\":\"Hello there!\", \"date\":Date()])\n<\/pre>\nThe userInfo<\/code> now takes [AnyHashable:Any]?<\/code> as an argument, which we provide as a dictionary literal in Swift. Note that the userInfo<\/code> values don’t need to be homogeneous (that’s where the Any<\/code> comes in); we are sending along a String<\/code> and a Date<\/code>.<\/p>\nHandling Notifications<\/h3>\n
The guard<\/code> construct serves as a good method to unwrap and verify that the expected data is in the userInfo<\/code>.<\/p>\n\n func catchNotification(notification:Notification) -> Void {\n print(\"Catch notification\")\n \n guard let userInfo = notification.userInfo,\n let message = userInfo[\"message\"] as? String,\n let date = userInfo[\"date\"] as? Date else {\n print(\"No userInfo found in notification\")\n return\n }\n \n let alert = UIAlertController(title: \"Notification!\",\n message:\"\\(message) received at \\(date)\",\n preferredStyle: UIAlertControllerStyle.alert)\n alert.addAction(UIAlertAction(title: \"OK\", style: UIAlertActionStyle.default, handler: nil))\n self.present(alert, animated: true, completion: nil)\n \n }\n<\/pre>\nTo verify that the guard<\/code> works properly switch out the Date()<\/code> in the call to post<\/code> with a String<\/code> or some other object. You should see No userInfo found in notification<\/code> printed to the console.<\/p>\nExample Source<\/h3>\n
You can try out the code above with a simple iOS project. Create a new Single View Application<\/b> and replace the contents of ViewController.swift<\/code> with the following:<\/p>\n\nimport UIKit\n\nclass ViewController: UIViewController {\n \n let myNotification = Notification.Name(rawValue:\"MyNotification\")\n\n override func viewDidLoad() {\n super.viewDidLoad()\n \n let nc = NotificationCenter.default\n nc.addObserver(forName:myNotification, object:nil, queue:nil, using:catchNotification)\n }\n \n override func viewDidAppear(_ animated: Bool) {\n super.viewDidAppear(animated)\n let nc = NotificationCenter.default\n nc.post(name:myNotification,\n object: nil,\n userInfo:[\"message\":\"Hello there!\", \"date\":Date()])\n }\n \n func catchNotification(notification:Notification) -> Void {\n print(\"Catch notification\")\n \n guard let userInfo = notification.userInfo,\n let message = userInfo[\"message\"] as? String,\n let date = userInfo[\"date\"] as? Date else {\n print(\"No userInfo found in notification\")\n return\n }\n \n let alert = UIAlertController(title: \"Notification!\",\n message:\"\\(message) received at \\(date)\",\n preferredStyle: UIAlertControllerStyle.alert)\n alert.addAction(UIAlertAction(title: \"OK\", style: UIAlertActionStyle.default, handler: nil))\n self.present(alert, animated: true, completion: nil)\n }\n}\n<\/pre>\nA few notes here:<\/p>\n
\n- `Notification` “names” are no longer strings, but are of type `Notification.Name`, hence why we declare `let myNotification = Notification.Name(rawValue:”MyNotification”)`. This allows us to use `myNotification` anywhere a `Notification.Name` is expected, i.e., the `NotificationCenter.addObserver` and `NotificationCenter.post` functions.\n
- We chose to have a separate `func` for `catchNotification` here rather than utilizing a trailing closure.\n<\/ul>\n
And that’s it! Simple and effective.<\/p>\n","protected":false},"excerpt":{"rendered":"
Editor’s Note: This is one of our most popular posts, so I wanted to take a moment and verify that the Swift 3.0 code presented below is still accurate with Swift 4.1. I’m happy to say it still is, so enjoy posting Notifications with userInfo in Swift 4! Swift 3.0 has brought a number of […]<\/p>\n","protected":false},"author":1,"featured_media":3108,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[63],"class_list":["post-3206","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-swift","tag-swift-notification-tutorial"],"_links":{"self":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/3206"}],"collection":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/comments?post=3206"}],"version-history":[{"count":10,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/3206\/revisions"}],"predecessor-version":[{"id":3416,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/3206\/revisions\/3416"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/media\/3108"}],"wp:attachment":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/media?parent=3206"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/categories?post=3206"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/tags?post=3206"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![\"Xcode](\"https:\/\/img.shields.io\/badge\/Xcode-8.0-blue.svg?style=flat\")
![\"Swift](\"https:\/\/img.shields.io\/badge\/Swift-3.0-orange.svg?style=flat\")
<\/p>\n![\"Xcode](\"https:\/\/img.shields.io\/badge\/Xcode-9.3-blue.svg?style=flat\")
![\"Swift](\"https:\/\/img.shields.io\/badge\/Swift-4.1-orange.svg?style=flat\")
<\/p>\n