ios - Detect volume button press

Question

Volume button notification function is not being called.

Code:

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")
}

listenVolumeButton() is being called in viewWillAppear

The code is not getting to the print statement "got in here", in either case.

I am trying two different ways to do it, neither way is working.

I have followed this: Detect iPhone Volume Button Up Press?

Answer 1

Using the second method, the value of the key path should be "outputVolume". That is the property we are observing. So change the code to,

var outputVolumeObserve: NSKeyValueObservation?
let audioSession = AVAudioSession.sharedInstance()

func listenVolumeButton() {
    do {
        try audioSession.setActive(true)
    } catch {}

    outputVolumeObserve = audioSession.observe(.outputVolume) { (audioSession, changes) in
        /// TODOs
    }
}