ProtocolFoundationEssentials
NotificationCenter.MessageIdentifier
iOS 26.0+
iPadOS 26.0+
Mac Catalyst 26.0+
macOS 26.0+
tvOS 26.0+
visionOS 26.0+
watchOS 26.0+
An optional identifier to associate a given message with a given type.
protocol MessageIdentifierOverview
Implement a MessageIdentifier to provide a typed, ergonomic experience at the call point, as described in SE-0299.
For example, given ExampleMessage with a Subject called ExampleSubject:
extension NotificationCenter.MessageIdentifier where Self == NotificationCenter.BaseMessageIdentifier<ExampleMessage> {
static var eventDidOccur: Self { .init() }
}This simplifies the call point for clients, as seen here:
let token = center.addObserver(of: exampleSubject, for: .eventDidOccur) { ... }