ios - 无法在 UILabel 中显示我的文本

Question

我不知道为什么我不能在我的 UILabel 中打印我的“pocetDatabaze3”。

这是我的代码:

@IBOutlet weak var aktualniPocet: UILabel!
var pocetDatabaze2 = 0
var pocetDatabaze3 = "dfh"

override func viewDidLoad() {
    super.viewDidLoad()

    if let url = NSURL(string: "http://servis.dronysitmp.cz/cteni_baterie.php") {
        let task = URLSession.shared.dataTask(with: url as URL, completionHandler: { (data, response, error) -> Void in
            //print(data)

            if let pocetDatabaze = NSString(data: data!, encoding: String.Encoding.ascii.rawValue){

                self.pocetDatabaze2 = Int(pocetDatabaze as String)!
                //self.pocetDatabaze3 = String(describing: pocetDatabaze)
            }

        }

        );
        task.resume()
    }

    pocetDatabaze3 = String(pocetDatabaze2 as Int)
    aktualniPocet.text = pocetDatabaze3

}

在 UILabel 中它显示“0”，但它应该是“25”。加载此 View 后，我还有两个操作。当我使用它们时，它会显示正确的值。剩下的就是:

@IBAction func odecteni(_ sender: UIButton) {
    pocetDatabaze2 = pocetDatabaze2 - 1
    self.pocetDatabaze3 = String(pocetDatabaze2 as Int)
    aktualniPocet.text = pocetDatabaze3
}

Answer 1

这是线程问题。 URLSession 是异步的，因此您必须在 completionHandler 中更新 UI。

let task = URLSession.shared.dataTask(with: url as URL, completionHandler: { (data, response, error) -> Void in
    //print(data)

    if let pocetDatabaze = NSString(data: data!, encoding: String.Encoding.ascii.rawValue) {

        self.pocetDatabaze2 = Int(pocetDatabaze as String)!
        self.pocetDatabaze3 = String(pocetDatabaze2 as Int)
        DispatchQueue.main.async {
            self.aktualniPocet.text = pocetDatabaze3
        }
    }

})

您需要调用 DispatchQueue.main 因为您应该在主线程中更新 UI。然后你可以注释掉其他两个调用。