Wrapping Notifications for Sendability

KeyboardDidShow.swift

// Example of wrapping `UIApplication.keyboardDidShowNotification` payload 

struct KeyboardDidShowPayload {
    let keyboardFrameBegin: CGRect?
    let keyboardFrameEnd: CGRect?
}

extension NotificationWrapper where Payload == KeyboardDidShowPayload {
    @MainActor static let keyboardDidShow: Self = .init(
        name: UIApplication.keyboardDidShowNotification,
        parser: NotificationParsing<KeyboardDidShowPayload>() { notification in
            guard let userInfo = notification.userInfo,
                  let begin = userInfo[UIResponder.keyboardFrameBeginUserInfoKey] as? NSValue,
                  let end = userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue else {
        return .init(keyboardFrameBegin: nil, keyboardFrameEnd: nil)
    }
            return .init(
                keyboardFrameBegin: begin.cgRectValue,
                keyboardFrameEnd: end.cgRectValue
            )
        }
    )
}

MyWindow.swift

// example call site
class MyWindow: UIWindow {
    func observe() async {
        for await payload in NotificationCenter.default.notifications(.keyboardDidShow) {
            print(payload.keyboardFrameBegin)
        }
    }
}

NotificationWrapper.swift

struct NotificationWrapper<Payload> {
    let name: Notification.Name
    let parser: NotificationParsing<Payload>
}

struct NotificationParsing<Payload>: @unchecked Sendable {
    let parse: (Notification) -> Payload
}

extension NotificationCenter {
    func notifications<Payload>(
        _ wrapper: NotificationWrapper<Payload>
    ) -> AsyncMapSequence<NotificationCenter.Notifications, Payload> {
        notifications(named: wrapper.name).map { wrapper.parser.parse($0) }
    }
}