How to post messages using NotificationCenter
Swift version: 5.1
iOS notifications are a simple and powerful way to send data in a loosely coupled way. That is, the sender of a notification doesn't have to care about who (if anyone) receives the notification, it just posts it out there to the rest of the app and it could be picked up by lots of things or nothing depending on your app's state.
As a basic example, you might want various parts of your app to do some work when the user logs in – you might want some views to refresh, you might want a database to update itself, and so on. To do this, just post a notification name like this:
let nc = NotificationCenter.default
nc.post(name: Notification.Name("UserLoggedIn"), object: nil)Note: it is preferable, for type safety, to define your notification names as static strings that belong to a class or struct or other global form so that you don't make a typo and introduce bugs.
To register to catch a notification being posted, use this:
nc.addObserver(self, selector: #selector(userLoggedIn), name: Notification.Name("UserLoggedIn"), object: nil)That will call a userLoggedIn() method when your notification is posted.
LEARN SWIFTUI FOR FREE I have a massive, free SwiftUI video collection on YouTube teaching you how to build complete apps with SwiftUI – check it out!
Available from iOS 2.0
Similar solutions…
- How to convert dates and times to a string using DateFormatter
- How to set local alerts using UNNotificationCenter
- How to render shadows using NSShadow and setShadow()
- How to create views in a loop using ForEach
- Building a menu using List
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
