音频未播放 Xcode 10.1 Swift 4

Question

I finally started learning to play sounds but I'm not succeeding in playing sounds in my app. I'm still on Xcode 10.1/Swift4 (not 4.2) as I'm not able to upgrade to Mojave/Catalina yet. I read quite a few posts about .setCategory(.playback, mode: .default) carrying a bug in Xcode 10.1 but solutions found are for Swift 4.2. Also category: and mode: are expected to be of type String ,but on docs the function is explained as:

func setCategory(_ category: AVAudioSession.Category, mode: AVAudioSession.Mode, options: AVAudioSession.CategoryOptions = []) throws

and they're not of type String . I'm a bit lost here.

My code doesn't throw any compiling error, but at runtime on console I get :

AVAudioSessionUtilities.mm:106:getUInt32: -- Category Value Converter failed to find a match for string "ambient"

What am I missing here? Can you please point me in the right direction to understand this category problem? As always thank you very much for your time and help.

This is the function that should play sounds :

static func playOnceSound(soundToPlay: String) {
       var player: AVAudioPlayer?
        guard let url = Bundle.main.url(forResource: soundToPlay, withExtension: "mp3") else { return }



        do {
//            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default) // Error: Type 'String' has no member 'playback'

            try AVAudioSession.sharedInstance().setCategory("ambient", mode: "default", options: .defaultToSpeaker)
            try AVAudioSession.sharedInstance().setActive(true)

            /* The following line is required for the player to work on iOS 11. Change the file type accordingly*/
            player = try AVAudioPlayer(contentsOf: url, fileTypeHint: AVFileType.mp3.rawValue)

            /* iOS 10 and earlier require the following line:
             player = try AVAudioPlayer(contentsOf: url, fileTypeHint: AVFileTypeMPEGLayer3) */

            guard let player = player else { return }
            player.numberOfLoops = 1
            player.volume = 1.0
            player.play()

        } catch let error {
            print(error.localizedDescription)
        }
    }

Answer 1

Have you tried inputting ambient & default this way, instead of using a string? Also, instantiating the audio session object before setCategory:

var audioSession: AVAudioSession?

func setup() {
    audioSession = AVAudioSession.sharedInstance()

    do {
        try audioSession.setCategory(AVAudioSession.Category.ambient, mode: .default, options: .defaultToSpeaker)
        try audioSession.setActive(true)
    }
    catch {
        print("Failed to set category", error.localizedDescription)
    }
}

Answer 2

@IBAction func doPlay1(_ sender: AnyObject) {
    do{
        self.audioPlayer = try AVAudioPlayer(contentsOf: URL.init(string: url)!)
        self.audioPlayer.prepareToPlay()
        self.audioPlayer.delegate = self
        self.audioPlayer.play()
    }catch{
        print(error.localizedDescription)
    }
}

Answer 3

So I just set it in AppDelegate didFinishLaunchingWithOptions as :

 do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        } catch let error1 as NSError{
            error = error1
            print("could not set session. err:\(error!.localizedDescription)")
        }
        do {
            try AVAudioSession.sharedInstance().setActive(true)
        } catch let error1 as NSError{
            error = error1
            print("could not active session. err:\(error!.localizedDescription)")
        } 

and rewrote the function as :

static func playOnceSound(soundToPlay: String) {
        if Sounds.player!.isPlaying == true {
            Sounds.player!.stop()
        }

        let url = URL(fileURLWithPath: Bundle.main.path(forResource: soundToPlay, ofType: "mp3")!)

        var error: NSError?

        do {
            Sounds.player = try AVAudioPlayer(contentsOf: url)
        } catch let error1 as NSError {
            error = error1
            Sounds.player = nil
        }

        if let err = error {
            print("audioPlayer error \(err.localizedDescription)")
            return
        } else {
            Sounds.player!.prepareToPlay()
        }
        //negative number means loop infinity
        Sounds.player!.numberOfLoops = 0
        Sounds.player!.volume = Sounds.volume
        Sounds.player!.play()

    }

Thanks for your help, and I hope this will be of help to others. Cheers.