Sample usage of AVAudioSessionInterruptionNotification

SampleAVAudioSessionInterruptionNotification.swift

func addInterruptionNotification() {
    // add audio session interruption notification
    NSNotificationCenter.defaultCenter().addObserver(self,
        selector: "handleInterruption:",
        name: AVAudioSessionInterruptionNotification,
        object: nil)
}

func handleInterruption(notification: NSNotification) {
    if notification.name != AVAudioSessionInterruptionNotification
        || notification.userInfo == nil{
        return
    }
    var info = notification.userInfo!
    var intValue: UInt = 0
    (info[AVAudioSessionInterruptionTypeKey] as NSValue).getValue(&intValue)
    if let type = AVAudioSessionInterruptionType.fromRaw(intValue) {
        switch type {
        case .Began:
            // interruption began
            println("began")
        case .Ended:
            // interruption ended
            println("ended")
        }
    }
}

It doesn't call on when interruption ends

interruption end events are not guaranteed:

Note: There is no guarantee that a begin interruption will have a corresponding end interruption. Your app needs to be aware of a switch to a foreground running state or the user pressing a Play button. In either case, determine whether your app should reactivate its audio session.

https://developer.apple.com/library/content/documentation/Audio/Conceptual/AudioSessionProgrammingGuide/HandlingAudioInterruptions/HandlingAudioInterruptions.html