Swift - Press Button (completion handler issue) - swift

Question

I want a user to press a button, it changes background color (to yellow), a WAV is played and on completion of the WAV the button reverts to its original color (to red). So have a completion handler around the sound. Have tried various combinations of the code below but the WAV plays and the button doesn't appear to change color.
Is this the wrong approach or am I doing something wrong? Don't want to have to put completion handlers around the color changes as that, I presume, is overkill.
Many thanks.
typealias CompletionHandler = (success:Bool) -> Void
#IBAction func fireButton(sender: AnyObject) {
playLaser( { (success)-> Void in
if success {
self.shots -= 1
self.labelShotsLeft.text = String(self.shots)
} else {
}
})
}
func playLaser(completionHandler: CompletionHandler) {
fireButton.layer.backgroundColor = UIColor.yellowColor().CGColor
let url = NSBundle.mainBundle().URLForResource("laser", withExtension: "wav")!
do {
player = try AVAudioPlayer(contentsOfURL: url)
guard let player = player else { return }
player.prepareToPlay()
player.play()
} catch let error as NSError {
print(error.description)
}
self.fireButton.layer.backgroundColor = UIColor.redColor().CGColor
completionHandler(success: true)
}

Answer 1

To detect AVAudioPlayer finish playing, you need to use AVAudioPlayerDelegate.
You may need to write something like this:
func playLaser(completionHandler: CompletionHandler) {
fireButton.layer.backgroundColor = UIColor.yellowColor().CGColor
let url = NSBundle.mainBundle().URLForResource("laser", withExtension: "wav")!
do {
player = try AVAudioPlayer(contentsOfURL: url)
guard let player = player else { return }
player.delegate = self //<- Sorry, this was missing in my first post
player.play()
} catch let error as NSError {
print(error.description)
}
audioPlayerCompletionHandler = completionHandler
}
var audioPlayerCompletionHandler: CompletionHandler?
func audioPlayerDidFinishPlaying(player: AVAudioPlayer, successfully flag: Bool) {
self.fireButton.layer.backgroundColor = UIColor.redColor().CGColor
audioPlayerCompletionHandler?(success: true)
}
(You need to add conformance to AVAudioPlayerDelegate to your ViewController's declaration header.)

Answer 2

Code does not magically pause and wait just because you say play.play() — that would be horrible! Thus, your so-called completion handler is not a completion handler at all. It runs immediately — that is, as soon you start playing. Your code does nothing about obtaining information as to when the audio player has finished playing.
For that, you need to configure a delegate and receive the delegate message that audio player emits when it finishes playing.

Answer 3

This is one of those questions which is a little more subtle than meets the eye. I tried putting three completion handlers around each task: change colour to yellow, play sound, change colour back to red. The code was being executed in the correct sequence as I NSLogged it but the button never changed colour due to screen updating controls. Here is the code that works that I hope other readers might find useful:
Swift 2.0
#IBAction func fireButton(sender: AnyObject) {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
dispatch_sync(dispatch_get_main_queue()) {
self.fireButton.layer.backgroundColor = UIColor.yellowColor().CGColor
}
self.playLaser( { (success)-> Void in
if success {
self.shots -= 1
} else {
}
})
dispatch_sync(dispatch_get_main_queue()) {
self.labelShotsLeft.text = String(self.shots)
self.fireButton.layer.backgroundColor = UIColor.redColor().CGColor
}
}
}
func playLaser(completion: (success: Bool) -> ()) {
let url = NSBundle.mainBundle().URLForResource("laser", withExtension: "wav")!
do {
player = try AVAudioPlayer(contentsOfURL: url)
guard let player = player else { return }
player.play()
completion(success: true)
} catch let error as NSError {
completion(success: false)
}
}
Swift 3.0
#IBAction func fireButton(_ sender: AnyObject) {
let fireQueue = DispatchQueue(label: "queueFirebutton")
fireQueue.async {
DispatchQueue.main.sync {
self.fireButtonDisabled()
}
DispatchQueue.main.sync {
self.playLaser()
self.shots -= 1
if self.shots <= 0 {
self.shots = 0
}
}
DispatchQueue.main.sync {
if self.shots < 0 { self.shots = 0}
self.labelShotsLeft.text = String(self.shots)
sleep(1)
self.fireButtonEnabled()
}
}
}
func playLaser() {
let url = Bundle.main.url(forResource: "laser", withExtension: "wav")!
do {
player = try AVAudioPlayer(contentsOf: url)
guard let player = player else { return }
player.play()
} catch {
}
}