ios - 如何在 Swift 的 UI 上呈现异步调用提供的数据？

Question

我已经设法将以下代码收集到我的 GameCenterHelper 类中。然而我完全迷失了 Swift 的 block 和completionHandlers。有人可以发布一个代码示例，如何在异步完成处理程序到达时访问它提供的数据吗？

class ShowHighscoresScene: SKScene {

override init(size: CGSize) {
  super.init(size: size)
  gameCenter.getHighscores()
  //what kind of parallel-thread-completionHandler-thingy goes here so I can show the highscores when the arrive, if the player is still using this scene?
}
...
}

class GameCenterHelper {
...
func getHighscores() {
    leaderboardReceived = nil
    let leaderboardRequest = GKLeaderboard() as GKLeaderboard!
    leaderboardRequest.identifier = "appId"
    if leaderboardRequest != nil
    {
        leaderboardRequest.loadScoresWithCompletionHandler({ (scores:[AnyObject]!, error:NSError!) -> Void in
            if (error != nil)
            {
                println("error in leaderboard highscore request")
                println(error.description)
            }
            else
            {
                self.leaderboardReceived = leaderboardRequest
            }

        })
    }
}
...

Answer 1

您可以将它放在 loadScoresWithCompletionHandler 的完成 block 中:

    leaderboardRequest.loadScoresWithCompletionHandler({ (scores:[AnyObject]!, error:NSError!) -> Void in
        if (error != nil)
        {
            println("error in leaderboard highscore request")
            println(error.description)
        }
        else
        {
            self.leaderboardReceived = leaderboardRequest

            // Your data-presenting code goes here:
            self.tableView.reloadData()
        }

    })