Question

我有一个应用程序，它从parse.com数据库中提取信息并将其传递给数组。当我从while循环中println（）这个数组时，它打印正常。当我尝试在while循环外打印时，它返回空。这是我的代码：

var players = [String]()
var total = [String]()

var addTotal:AnyObject!
var addTotalFinal:Int!

var addPlayers:AnyObject!
var addPlayersFinal:Array<Int>!

@IBOutlet weak var tableView: UITableView!
var test: AnyObject!
override func viewDidLoad() {
    super.viewDidLoad()

     Parse.setApplicationId("KZ758LUTQZQ9Kl69mBDkv7BNLGHyXeKmqtFf7GmO", clientKey: "lOK5rg7wKeTRXZGV7MZBlQ5PTpNlGO0mkgtLkLgH")

    var query = PFQuery(className:"runningTotal")
    query.whereKey("total", notEqualTo: 0)
    query.findObjectsInBackgroundWithBlock
    {
        (objects: [AnyObject]!, error: NSError!) -> Void in
        if error == nil
        {

            var i = 0

            while i < objects.count
            {

            self.addTotal = objects[i]["total"]
            self.addTotalFinal = self.addTotal as Int

            self.addPlayers = objects[i]["players"]
            self.addPlayersFinal = self.addPlayers as Array

            self.players.append("\(self.addPlayersFinal)")
            self.total.append("\(self.addTotalFinal)")

                ++i
            }



        }
        else
        {

        }




    }

    navigationItem.title = "\(players)"



 }


func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int
{
    return players.count
}


func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell
{
    var cell = tableView.dequeueReusableCellWithIdentifier("MyCell", forIndexPath: indexPath) as UITableViewCell
    cell.textLabel.text = "\(players[indexPath.row]) - \(total[indexPath.row])"

    return cell

}

while语句中的println（）返回

[[1, 11, 12, 24, 25]]
[2]

[[1, 11, 12, 24, 25], [1, 5, 24, 25, 31]]
[2, 4]

[[1, 11, 12, 24, 25], [1, 5, 24, 25, 31], [2, 12, 25, 15, 31]]
[2, 4, -1]

[[1, 11, 12, 24, 25], [1, 5, 24, 25, 31], [2, 12, 25, 15, 31], [24, 22, 25, 31, 20]]
[2, 4, -1, -6]

[[1, 11, 12, 24, 25], [1, 5, 24, 25, 31], [2, 12, 25, 15, 31], [24, 22, 25, 31, 20], [1, 2, 3, 4, 5]]
[2, 4, -1, -6, 5]

[[1, 11, 12, 24, 25], [1, 5, 24, 25, 31], [2, 12, 25, 15, 31], [24, 22, 25, 31, 20], [1, 2, 3, 4, 5], [1, 10, 11, 2, 12]]
[2, 4, -1, -6, 5, 1]

这是有道理的，因为有六次迭代。但是，如果我在viewDidLoad语句内而不是在while语句内打印，则返回 [] []

非常感谢任何帮助。

Answer 1

问题是您还没有理解线程/异步执行的工作原理。让我们更简单。这是伪代码：

func viewDidLoad {
    doStepOne() // you configure your query here
    doStepTwoWithAsynchBlock {
        doStepTwo() // your while loop is here
    }
    doStepThree() // your failing println is here
}

这将按doStepOne()，doStepThree()，doStepTwo()的顺序执行。因此，如果doStepThree()尝试获取doStepTwo()设置的值，那么它还没有准备好。

asynch块是将发生的事情，将来的某个时间 - 在所有其他代码完成之后，包括{{1}的其余部分}}

迅速范围问题

1 个答案: