swift - Why does declaring WKExtendedRuntimeSession inside a class cause a fatal error?

Question

I'm new to Swift and came up with the following class to manage an extended runtime session (alarm):

import Foundation
import WatchKit

class Alarm: ObservableObject {
    private var session: WKExtendedRuntimeSession!

    func start() {
        session = WKExtendedRuntimeSession()
        session.start(at: Date())
    }

    func stop() {
        session.notifyUser(hapticType: .stop)
        session.invalidate()
    }
}

However, it fails with the following error:

Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value: file

Why is that? It works if I put the session declaration out of the class.

question from:https://stackoverflow.com/questions/65947905/why-does-declaring-wkextendedruntimesession-inside-a-class-cause-a-fatal-error

Answer 1

Waitting for answers