Question

未调用音量按钮通知功能。

代码：

func listenVolumeButton(){
    // Option #1
    NSNotificationCenter.defaultCenter().addObserver(self, selector: "volumeChanged:", name: "AVSystemController_SystemVolumeDidChangeNotification", object: nil)
    // Option #2
    var audioSession = AVAudioSession()
    audioSession.setActive(true, error: nil)
    audioSession.addObserver(self, forKeyPath: "volumeChanged", options: NSKeyValueObservingOptions.New, context: nil)
}

override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void>) {
    if keyPath == "volumeChanged"{
        print("got in here")
    }
}

func volumeChanged(notification: NSNotification){
   print("got in here")
}

在viewWillAppear中调用

listenVolumeButton()

在任何一种情况下，代码都没有进入打印语句"got in here"。

我正在尝试两种不同的方法，但两种方式都不起作用。

我已经遵循了这个：Detect iPhone Volume Button Up Press?

Answer 1

使用第二种方法，密钥路径的值应为"outputVolume"。这是我们正在观察的财产。所以将代码更改为，

func listenVolumeButton(){

    let audioSession = AVAudioSession.sharedInstance()
    audioSession.setActive(true, error: nil)
    audioSession.addObserver(self, forKeyPath: "outputVolume",
        options: NSKeyValueObservingOptions.New, context: nil)
}

override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject,
    change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void>) {
    if keyPath == "outputVolume"{
        print("got in here")
    }
}

Answer 2

上面的代码在Swift 3中不起作用，在这种情况下，试试这个：

func listenVolumeButton() {
   do {
    try audioSession.setActive(true)
   } catch {
    print("some error")
   }
   audioSession.addObserver(self, forKeyPath: "outputVolume", options: NSKeyValueObservingOptions.new, context: nil)
}

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
  if keyPath == "outputVolume" {
    print("got in here")
  }
}

Answer 3

使用此代码，您可以在用户点击音量硬件按钮时进行监听。

class VolumeListener {
    static let kVolumeKey = "volume"

    static let shared = VolumeListener()

    private let kAudioVolumeChangeReasonNotificationParameter = "AVSystemController_AudioVolumeChangeReasonNotificationParameter"
    private let kAudioVolumeNotificationParameter = "AVSystemController_AudioVolumeNotificationParameter"
    private let kExplicitVolumeChange = "ExplicitVolumeChange"
    private let kSystemVolumeDidChangeNotificationName = NSNotification.Name(rawValue: "AVSystemController_SystemVolumeDidChangeNotification")

    private var hasSetup = false

    func start() {
        guard !self.hasSetup else {
            return
        }

        self.setup()
        self.hasSetup = true

    }

    private func setup() {
        guard let rootViewController = UIApplication.shared.windows.first?.rootViewController else {
            return
        }

        let volumeView = MPVolumeView(frame: CGRect.zero)
        volumeView.clipsToBounds = true
        rootViewController.view.addSubview(volumeView)

        NotificationCenter.default.addObserver(
            self,
            selector: #selector(self.volumeChanged),
            name: kSystemVolumeDidChangeNotificationName,
            object: nil
        )

        volumeView.removeFromSuperview()
    }

    @objc func volumeChanged(_ notification: NSNotification) {
        guard let userInfo = notification.userInfo,
            let volume = userInfo[kAudioVolumeNotificationParameter] as? Float,
            let changeReason = userInfo[kAudioVolumeChangeReasonNotificationParameter] as? String,
            changeReason == kExplicitVolumeChange
            else {
                return
        }

        NotificationCenter.default.post(name: "volumeListenerUserDidInteractWithVolume", object: nil,
                                        userInfo: [VolumeListener.kVolumeKey: volume])
    }
}

要收听，您只需添加观察者：

NotificationCenter.default.addObserver(self, selector: #selector(self.userInteractedWithVolume),
                                           name: "volumeListenerUserDidInteractWithVolume", object: nil)

您可以通过检查userInfo来访问音量值：

@objc private func userInteractedWithVolume(_ notification: Notification) {
    guard let volume = notification.userInfo?[VolumeListener.kVolumeKey] as? Float else {
        return
    }

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

Answer 4

import AVFoundation
import MediaPlayer

override func viewDidLoad() {
  super.viewDidLoad()
  let volumeView = MPVolumeView(frame: CGRect.zero)
  for subview in volumeView.subviews {
    if let button = subview as? UIButton {
      button.setImage(nil, for: .normal)
      button.isEnabled = false
      button.sizeToFit()
    }
  }
  UIApplication.shared.windows.first?.addSubview(volumeView)
  UIApplication.shared.windows.first?.sendSubview(toBack: volumeView)
}

override func viewWillAppear(_ animated: Bool) {
  super.viewWillAppear(animated)
  AVAudioSession.sharedInstance().addObserver(self, forKeyPath: "outputVolume", options: NSKeyValueObservingOptions.new, context: nil)
  do { try AVAudioSession.sharedInstance().setActive(true) }
  catch { debugPrint("\(error)") }   
}

override func viewDidDisappear(_ animated: Bool) {
  super.viewDidDisappear(animated)
  AVAudioSession.sharedInstance().removeObserver(self, forKeyPath: "outputVolume")
  do { try AVAudioSession.sharedInstance().setActive(false) } 
  catch { debugPrint("\(error)") }
}

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
  guard let key = keyPath else { return }
  switch key {
    case "outputVolume":
      guard let dict = change, let temp = dict[NSKeyValueChangeKey.newKey] as? Float, temp != 0.5 else { return }
      let systemSlider = MPVolumeView().subviews.first { (aView) -> Bool in
        return NSStringFromClass(aView.classForCoder) == "MPVolumeSlider" ? true : false
     } as? UISlider
      systemSlider?.setValue(0.5, animated: false)
      guard systemSlider != nil else { return }
      debugPrint("Either volume button tapped.")
    default:
      break
  } 
}

观察新值时，我将系统音量设置回0.5。这可能会激怒用户同时使用音乐，因此我不建议在制作中使用自己的答案。

Answer 5

如果有兴趣，这里有一个 RxSwift 版本。

func volumeRx() -> Observable<Void> {
    Observable<Void>.create {
        subscriber in
        
        let audioSession = AVAudioSession.sharedInstance()
        do {
            try audioSession.setActive(true)
        } catch let e {
            subscriber.onError(e)
        }

        let outputVolumeObserve = audioSession.observe(\.outputVolume) {
            (audioSession, changes) in
            subscriber.onNext(Void())
        }
        
        return Disposables.create {
            outputVolumeObserve.invalidate()
        }
    }
}

用法

volumeRx()
   .subscribe(onNext: {
      print("Volume changed")
   }).disposed(by: disposeBag)

检测音量按钮按下

5 个答案: