在iOS 14上从未触发SystemVolumeDidChangeNotification

目标是监视卷更改事件及其值。跟着导游走

在iOS 14上。*当我尝试观察卷更改事件时，该事件似乎在卷更改后从未被触发

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)")
}

---

beginReceivingRemoteControlEvents

需要首先调用

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)
}

覆盖函数视图显示（uu动画：Bool）{
super.viewdide显示（动画）
UIApplication.shared.beginReceivingRemoteControlEvents（）//谢谢，我想知道为什么在iOS 14.1之前我们从来不需要使用它。