#selector<\/code> directive, like this:<\/p>\n\nlet nc = NSNotificationCenter.defaultCenter()\nnc.addObserver(self, \n selector: #selector(ViewController.catchNotification),\n name: \"MyNotification\", \n object: nil)\n<\/pre>\nIn this example we’re instructing the notification center to deliver MyNotification<\/code> notifications to the catchNotification<\/code> function of the ViewController<\/code> class.<\/p>\nPost It!<\/h3>\n
Now, let’s look at posting<\/i> (sending) a notification:<\/p>\n\nlet nc = NSNotificationCenter.defaultCenter()\nnc.postNotificationName(\"MyNotification\",\n object: nil,\n userInfo: [\"message\":\"Hello there!\", \"date\":NSDate()])\n<\/pre>\nThe userInfo<\/code> still takes [NSObject : AnyObject]?<\/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 AnyObject<\/code> comes in); we are sending along a String<\/code> and an NSDate<\/code>.<\/p>\nHandling Notifications<\/h3>\n
The guard<\/code> construct did not exist in Swift when I wrote the original code used to pull apart the userInfo<\/code> data, but it serves as a good method to unwrap and verify that the expected data is in the userInfo<\/code>.<\/p>\n\n func catchNotification(notification:NSNotification) -> 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? NSDate 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.presentViewController(alert, animated: true, completion: nil)\n \n }\n<\/pre>\nTo verify that the guard<\/code> works properly switch out the NSDate()<\/code> in the call to postNotificationName<\/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 override func viewDidLoad() {\n super.viewDidLoad()\n \n let nc = NSNotificationCenter.defaultCenter()\n nc.addObserver(self,\n selector: #selector(ViewController.catchNotification),\n name: \"MyNotification\",\n object: nil)\n \n }\n \n override func viewDidAppear(animated: Bool) {\n super.viewDidAppear(animated)\n let nc = NSNotificationCenter.defaultCenter()\n nc.postNotificationName(\"MyNotification\",\n object: nil,\n userInfo: [\"message\":\"Hello there!\",\n \"date\":NSDate()])\n }\n \n func catchNotification(notification:NSNotification) -> 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? NSDate 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.presentViewController(alert, animated: true, completion: nil)\n }\n}\n<\/pre>\n","protected":false},"excerpt":{"rendered":"Looking for help using notifications with Swift 3.0? Head on over here where we go over the latest Swift 3.0 changes. When I sit down to blog I never know what will be a popular topic and what won’t. One that definitely surprised me was how popular the original NSNotifications with userInfo in Swift would […]<\/p>\n","protected":false},"author":1,"featured_media":2826,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-2794","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-swift"],"_links":{"self":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/2794"}],"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=2794"}],"version-history":[{"count":11,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/2794\/revisions"}],"predecessor-version":[{"id":2825,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/2794\/revisions\/2825"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/media\/2826"}],"wp:attachment":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/media?parent=2794"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/categories?post=2794"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/tags?post=2794"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![\"Xcode](\"https:\/\/img.shields.io\/badge\/Xcode-7.3-blue.svg?style=flat\")
![\"Swift](\"https:\/\/img.shields.io\/badge\/Swift-2.2-orange.svg?style=flat\")
<\/p>\n