Thank you for your kind reply. When I made the changes as you suggested, I was able to use DispatchNotificationCenter. I had overlooked the Availability in the documentation. Thanks,

Thanks for your reply eskimo. My target platform is iOS. And I am using network extension (packet tunnel provider). I would like to know how startTunnel() and stopTunnel(), which exist in the NEPacketTunnelProvider, use NotificationCenter to send messages to the ViewController. Kind regards

Thank you so much eskimo. Thanks to your answers, I will be able to do what I want to do!