AVAudioPlayer播放音频文件时没声音

AVAudioPlayer播放一个mp3文件时，居然没有声音。mp3文件是放在工程里面的，路径没有错误但就是死活没有声音。

func playSound() {
let notifyUrl = NSBundle.mainBundle().pathForResource("notify", ofType: "mp3")
//let notifyUrl = NSBundle.mainBundle().resourcePath?.stringByAppendingPathComponent("notify.mp3")
if let mp3 = notifyUrl {
let url = NSURL(fileURLWithPath: mp3)

//            var filemanager = NSFileManager()
//            let result = filemanager.fileExistsAtPath(mp3)
//            println("result=\(result)")

AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback, error: nil)

var error:NSError?
var avAudioPlayer = AVAudioPlayer(contentsOfURL: url, error: &error)
if error != nil {
println(error)
} else {
avAudioPlayer.volume = 1.0
avAudioPlayer.prepareToPlay()
avAudioPlayer.play()
}
}
}

解决方法是把avAudioPlayer定义为全局变量的时候就有声音了，是不是很神奇。应该是被内存回收了所以没有声音，记得要定义为全局变量

var avAudioPlayer:AVAudioPlayer?
func playSound() {
let notifyUrl = NSBundle.mainBundle().pathForResource("notify", ofType: "mp3")
//let notifyUrl = NSBundle.mainBundle().resourcePath?.stringByAppendingPathComponent("notify.mp3")
if let mp3 = notifyUrl {
let url = NSURL(fileURLWithPath: mp3)

//            var filemanager = NSFileManager()
//            let result = filemanager.fileExistsAtPath(mp3)
//            println("result=\(result)")

AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryPlayback, error: nil)

var error:NSError?
//var avAudioPlayer = AVAudioPlayer(contentsOfURL: url, error: &error)
avAudioPlayer = AVAudioPlayer(contentsOfURL: url, error: &error)
if error != nil {
println(error)
} else {
avAudioPlayer?.volume = 1.0
avAudioPlayer?.prepareToPlay()
avAudioPlayer?.play()
}
}
}