SystemVolumeDidChangeNotification never get triggered on iOS 14

Question

an alternative title is "Why AVSystemController_AudioVolumeNotificationParameter notification event never get triggered?"

The goal is to monitor the volume change event and its value. Followed the guide at detect up volume change swift.

On iOS 14.* when I try to observe volume change event, the event seems to never get triggered after volume change.

import MediaPlayer

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    NotificationCenter.default.addObserver(self, selector: #selector(volumeChange(_:)), name: Notification.Name(rawValue: "AVSystemController_SystemVolumeDidChangeNotification"), object: nil)
}

@objc func volumeChange(_ notification: NSNotification) {
    let userInfo = notification.userInfo!
    let volume = userInfo["AVSystemController_AudioVolumeNotificationParameter"] as! Double

    print("volume:\(volume)")
}

Answer 1

beginReceivingRemoteControlEvents need to be called first.

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    UIApplication.shared.beginReceivingRemoteControlEvents() // <- THIS LINE

    NotificationCenter.default.addObserver(self, selector: #selector(volumeChange(_:)), name: Notification.Name(rawValue: "AVSystemController_SystemVolumeDidChangeNotification"), object: nil)
}

Do not forget to remove the observer after the view disappeared.