iOS标签无法使用Swift中的功能更新文本 [英] iOS label does not update text with function in Swift

问题描述

这个看似简单的问题使我发疯……我正在玩SwiftyJSON来获取远程数据，这是我在Swift中的ViewController类的摘录:

This seemingly simple issue is driving me crazy... I am playing around with SwiftyJSON to grab remote data and here is a snippet from my ViewController class in Swift:

override func viewDidLoad() {
    super.viewDidLoad()

    self.statusLabel.text = "welcome"

    RemoteDataManager.getStatusUpdateFromURL { (statusData) -> Void in
        let json = JSON(data: statusData)
        self.statusLabel.text = "this does not work"
        self.statusLabel.text = self.getMostRecentStatusUpdate(json) // also does not work
    }

}

statusLabel文本设置为欢迎"，但此后不会更改.有趣的是，我放在func getMostRecentStatusUpdate(_:)和println()中的任何内容都正确地打印到了控制台，即使它来自远程json源(即我知道此功能也可以).我的问题是我无法将文本打印到UILabel而不是控制台上.我没有收到任何错误消息.

The statusLabel text is set to "welcome" but does not change afterwards. Funny though, anything I put inside func getMostRecentStatusUpdate(_:) with println() is printed to the console correctly, even if it comes from the remote json source (i.e. I know that this function works). My problem is that I cannot get the text printed to a UILabel instead of the console. I do not get any error messages.

我还不太熟悉像MyClass.myMethod { (myData) -> Void in .... }这样的Swift函数，我不明白这里出了什么问题.有什么想法吗?

I am not yet really familiar with the sort of Swift function like MyClass.myMethod { (myData) -> Void in .... } and I don't understand what's going wrong here. Any ideas?

推荐答案

UIKit不是线程安全的，只能从主线程进行更新.下载是在后台线程上完成的，您不能从那里更新UI.试试:

UIKit is not thread safe and should only be updated from the main thread. Downloads are done on background thread, and you cannot update UI from there. Try:

override func viewDidLoad() {
    super.viewDidLoad()

    self.statusLabel.text = "welcome"

    RemoteDataManager.getStatusUpdateFromURL { (statusData) -> Void in
        let json = JSON(data: statusData)

        dispatch_async(dispatch_get_main_queue()) {
            self.statusLabel.text = "this does not work"
            self.statusLabel.text = self.getMostRecentStatusUpdate(json) // also does not work
        }
    }
}

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