Swift 2迁移问题

这是带有Swift 2.0的do / try / catch实现的updateAction（）函数：

func updateAction(){    var firstRandomNumber = Int(arc4random_uniform(5))    var firstCardString:String = String(self.cardNamesArray[firstRandomNumber])    var secondRandomNumber = Int(arc4random_uniform(5))    var secondCardString:String = String(self.cardNamesArray[secondRandomNumber])    self.firstCardImageView.image = UIImage(named: firstCardString)    self.secondCardImageView.image = UIImage(named: secondCardString)    let fileLocation = NSBundle.mainBundle().pathForResource("sound", ofType: ".mp3")    do {        player = try AVAudioPlayer(contentsOfURL: NSURL(fileURLWithPath: fileLocation!))        try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryAmbient)        try AVAudioSession.sharedInstance().setActive(true)    }    catch {        print("Something bad happened. Try catching specific errors to narrow things down")    }    player.play()    let num = firstRandomNumber + secondRandomNumber + 2    self.label.text = "The sum is (num)"}