Play/Pause callback not getting called when using MPRemoteCommandCenter
<p>I am building a music player app, and everything is working fine. I have been using the system music player so far, but now want to switch over to use an application music player instead, and that's where I'm running into problems - for the life of me I can't figure out how to get my play/pause callback to be called from the iOS control center. Here's the code I'm using in my main view controller:</p>

<pre><code>override func viewDidLoad() {
    super.viewDidLoad()

    self.musicPlayer = MPMusicPlayerController.applicationMusicPlayer()

    self.registerForMediaPlayerNotifications()
    UIApplication.sharedApplication().beginReceivingRemoteControlEvents()

    let commandCenter = MPRemoteCommandCenter.sharedCommandCenter()

    commandCenter.previousTrackCommand.enabled = false
    commandCenter.previousTrackCommand.addTarget(self, action: "previousTrack")
    commandCenter.nextTrackCommand.enabled = false
    commandCenter.nextTrackCommand.addTarget(self, action: "nextTrack")
    commandCenter.togglePlayPauseCommand.enabled = true
    commandCenter.togglePlayPauseCommand.addTarget(self, action: "playOrPauseMusic")
    commandCenter.pauseCommand.addTarget(self, action: "playOrPauseMusic")
    commandCenter.pauseCommand.enabled = true
    commandCenter.playCommand.addTarget(self, action: "playOrPauseMusic")
    commandCenter.playCommand.enabled = true

    [...]
}


func previousTrack() {
}

func nextTrack() {
}

func playOrPauseMusic() {
   print("playOrPause")
}
</code></pre>