Why does Swift AVAudioPlayer not change state after MPRemoteCommandCenter play command? - ios

Question

The environment for this is iOS 13.6 and Swift 5. I have a very simple app that successfully plays an MP3 file in the foreground or background. I added MPRemoteCommandCenter play and pause command handlers to it. I play the sound file in the foreground and then pause it.
When I tap the play button from the lock screen, my code calls audioPlayer.play(), which returns true. I hear the sound start playing again, but the currentTime of the player does not advance. After that, the play and pause buttons on the lock screen do nothing. When I foreground the app again, the play button plays from where it was before I went to the lock screen.
Here is my AudioPlayer class:
import AVFoundation
import MediaPlayer
class AudioPlayer: RemoteAudioCommandDelegate {
var audioPlayer = AVAudioPlayer()
let remoteCommandHandler = RemoteAudioCommandHandler()
var timer:Timer!
func play(title: String) {
let path = Bundle.main.path(forResource: title, ofType: "mp3")!
let url = URL(fileURLWithPath: path)
do {
try AVAudioSession.sharedInstance().setCategory(AVAudioSession.Category.playback)
try AVAudioSession.sharedInstance().setActive(true)
audioPlayer = try AVAudioPlayer(contentsOf: url)
remoteCommandHandler.delegate = self
remoteCommandHandler.enableDisableRemoteCommands(true)
timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(updateNowPlayingInfo), userInfo: nil, repeats: true)
} catch let error as NSError {
print("error = \(error)")
}
}
func play() {
print ("audioPlayer.play() returned \(audioPlayer.play())")
}
func pause() {
audioPlayer.pause()
}
func stop() {
audioPlayer.stop()
}
func currentTime() -> TimeInterval {
return audioPlayer.currentTime
}
func setCurrentTime(_ time:TimeInterval) {
audioPlayer.currentTime = time
}
#objc func updateNowPlayingInfo() {
// Hard-code the nowPlayingInfo since this is a simple test app
var nowPlayingDict =
[MPMediaItemPropertyTitle: "Tin Man",
MPMediaItemPropertyAlbumTitle: "The Complete Greatest Hits",
MPMediaItemPropertyAlbumTrackNumber: NSNumber(value: UInt(10) as UInt),
MPMediaItemPropertyArtist: "America",
MPMediaItemPropertyPlaybackDuration: 208,
MPNowPlayingInfoPropertyPlaybackRate: NSNumber(value: 1.0 as Float)] as [String : Any]
nowPlayingDict[MPNowPlayingInfoPropertyElapsedPlaybackTime] = NSNumber(value: audioPlayer.currentTime as Double)
MPNowPlayingInfoCenter.default().nowPlayingInfo = nowPlayingDict
}
}
Here is my RemoteCommandHandler class:
import Foundation
import MediaPlayer
protocol RemoteAudioCommandDelegate: class {
func play()
func pause()
}
class RemoteAudioCommandHandler: NSObject {
weak var delegate: RemoteAudioCommandDelegate?
var remoteCommandCenter = MPRemoteCommandCenter.shared()
var playTarget: Any? = nil
var pauseTarget: Any? = nil
func enableDisableRemoteCommands(_ enabled: Bool) {
print("Called with enabled = \(enabled)")
remoteCommandCenter.playCommand.isEnabled = enabled
remoteCommandCenter.pauseCommand.isEnabled = enabled
if enabled {
addRemoteCommandHandlers()
} else {
removeRemoteCommandHandlers()
}
}
fileprivate func addRemoteCommandHandlers() {
print( "Entered")
if playTarget == nil {
print( "Adding playTarget")
playTarget = remoteCommandCenter.playCommand.addTarget { (event) -> MPRemoteCommandHandlerStatus in
print("addRemoteCommandHandlers calling delegate play")
self.delegate?.play()
return .success
}
}
if pauseTarget == nil {
print( "Adding pauseTarget")
pauseTarget = remoteCommandCenter.pauseCommand.addTarget { (event) -> MPRemoteCommandHandlerStatus in
print("addRemoteCommandHandlers calling delegate pause")
self.delegate?.pause()
return .success
}
}
}
fileprivate func removeRemoteCommandHandlers() {
print( "Entered")
if playTarget != nil {
print( "Removing playTarget")
remoteCommandCenter.playCommand.removeTarget(playTarget)
playTarget = nil
}
if pauseTarget != nil {
print( "Removing pauseTarget")
remoteCommandCenter.pauseCommand.removeTarget(pauseTarget)
pauseTarget = nil
}
}
}
I will gladly supply further required info, because I'm baffled at why this relatively straightforward code (in my mind) code doesn't work.
Assistance is much appreciated!

Answer 1

After some more debugging, I found that the AVAudioPlayer started to play the sound from the lock screen, but stopped again shortly after.
I mitigated the problem by adding a Timer. The timer checks if the last command by the user was play, but the sound is not playing. I also change the status when the user selects pause or the song stops playing at its natural end.
I am still at a loss for an actual fix for this problem.