对您的代码进行了修改：

import UIKit
import AVFoundation

class ViewController: UIViewController {

    var audioPlayer = AVAudioPlayer()

    override func viewDidLoad() {
        super.viewDidLoad()

        var alertSound = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("button-09", ofType: "wav"))
        println(alertSound)

        // Removed deprecated use of AVAudioSessionDelegate protocol
        AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback, error: nil)
        AVAudioSession.sharedInstance().setActive(true, error: nil)

        var error:NSError?
        audioPlayer = AVAudioPlayer(contentsOfURL: alertSound, error: &error)
        audioPlayer.prepareToPlay()
        audioPlayer.play()
    }

}

Swift 3和Swift 4.1：

import UIKit
import AVFoundation

class ViewController: UIViewController {
    private var audioPlayer: AVAudioPlayer?

    override func viewDidLoad() {
        super.viewDidLoad()

        let alertSound = URL(fileURLWithPath: Bundle.main.path(forResource: "button-09", ofType: "wav")!)
        print(alertSound)

        try! AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback)
        try! AVAudioSession.sharedInstance().setActive(true)

        try! audioPlayer = AVAudioPlayer(contentsOf: alertSound)
        audioPlayer!.prepareToPlay()
        audioPlayer!.play()
    }
}