如何使用Sprite Kit和Swift在游戏中设置高分

var playerScore = 0func playerScoreUpdate() {    let highScore = NSUserDefaults().integerForKey("highscore")    if playerScore > highScore {         NSUserDefaults().setInteger(playerScore, forKey: "highscore")    }    playerScorelabel.text = "Score: (playerScore)"}playerScore = 200playerScoreUpdate()println( NSUserDefaults().integerForKey("highscore") )  // 200playerScore = 180playerScoreUpdate()println( NSUserDefaults().integerForKey("highscore") )  // 200playerScore = 250playerScoreUpdate()println( NSUserDefaults().integerForKey("highscore") )  // 250highScoreLabel.text = "HighScore: " + NSUserDefaults().integerForKey("highscore").description