Swift 3.0 标签变为空白（零值？）

Question

我是新手 Swift，我正在尝试制作一个允许用户将事件信息输入文本字段的应用程序，然后当他们按下按钮时，该信息将显示在标签中一个单独的视图。但是，我目前遇到一个问题，当我在模拟器中单击按钮时，在每个字段中输入信息后，我只得到一个完全空白的视图，而不是显示信息的标签。

这是输入信息的控制器代码：

import UIKit

class CreateEventController: UIViewController {

    @IBOutlet weak var TitleTxt: UITextField!
    @IBOutlet weak var CityTxt: UITextField!
    @IBOutlet weak var CountryTxt: UITextField!
    @IBOutlet weak var VenueTxt: UITextField!
    @IBOutlet weak var TimeTxt: UITextField!
    @IBOutlet weak var UrlTxt: UITextField!

    @IBAction func SaveEventBtn(_ sender: UIButton) {

        if TitleTxt.text!.isEmpty || CityTxt.text!.isEmpty || 
    CountryTxt.text!.isEmpty || VenueTxt.text!.isEmpty ||
        TimeTxt.text!.isEmpty || UrlTxt.text!.isEmpty{

            let alert = UIAlertController(title: "Missing values", message: "Please populate all fields", preferredStyle: UIAlertControllerStyle.alert)

            alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler: nil))

            self.present(alert, animated: true, completion: nil)

        }

        else {

            print("The event title is \((TitleTxt.text)!)")

            func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) 
            {
                if (segue.identifier == "CreateEvntBtn") {
                    let destVC = segue.destination as! CreatedEventController

                    destVC.CrTitle = TitleTxt.text!
                    destVC.CrCity = CityTxt.text!
                    destVC.CrCountry = CountryTxt.text!
                    destVC.CrVenue = VenueTxt.text!
                    destVC.CrTime = TimeTxt.text!
                    destVC.CrUrl = UrlTxt.text!

                }
            }

        }

    }

}

这里是应该显示信息的视图控制器：

import UIKit

class CreatedEventController: UIViewController {


    @IBOutlet weak var CrTitleLbl: UILabel!
    @IBOutlet weak var CrCityLbl: UILabel!
    @IBOutlet weak var CrCountryLbl: UILabel!
    @IBOutlet weak var CrVenueLbl: UILabel!
    @IBOutlet weak var CrTimeLbl: UILabel!
    @IBOutlet weak var CrUrlLbl: UILabel!

    var CrTitle, CrCity, CrCountry, CrVenue, CrTime, CrUrl : String!

    override func viewDidLoad() {
        super.viewDidLoad()

        CrTitleLbl.text = CrTitle
        CrCityLbl.text = CrCity
        CrCountryLbl.text = CrCountry
        CrVenueLbl.text = CrVenue
        CrTimeLbl.text = CrTime
        CrUrlLbl.text = CrUrl
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }


}

我确定我遗漏了一些非常简单的东西，但我们将不胜感激。干杯！

Answer 1

您的 prepareForSegue 函数嵌套在另一个函数中。它需要处于 class 的级别。将其移到 SaveEventBtn.

之外

此外，您需要实际执行转场。在您当前 prepareForSegue 的位置，添加 performSegue(withIdentifier: "mySegueID", sender: nil)。请注意，mySegueID 是您在情节提要中创建的转场的名称。您目前拥有的它与按钮操作相同，可能是这种情况，但您可能应该将其命名为其他名称。

此外，为了让你的代码在未来更易读，避免你自己因错误而头疼，Swift的标准是让变量名（TitleTxt，CountryTxt）和函数名称 (SaveEventBtn) 驼峰式大小写 (titleTextField, countryTextField, saveTapped).

Answer 2

首先，您想覆盖 prepare(for:sender:)，而不是创建嵌套。其次，您要调用 performSegue，这将启动导航：

import UIKit

class CreateEventController: UIViewController {

    @IBOutlet weak var TitleTxt: UITextField!
    @IBOutlet weak var CityTxt: UITextField!
    @IBOutlet weak var CountryTxt: UITextField!
    @IBOutlet weak var VenueTxt: UITextField!
    @IBOutlet weak var TimeTxt: UITextField!
    @IBOutlet weak var UrlTxt: UITextField!

    @IBAction func SaveEventBtn(_ sender: UIButton) {

        if TitleTxt.text!.isEmpty || CityTxt.text!.isEmpty || 
           CountryTxt.text!.isEmpty || VenueTxt.text!.isEmpty ||
           TimeTxt.text!.isEmpty || UrlTxt.text!.isEmpty {

            let alert = UIAlertController(title: "Missing values", message: "Please populate all fields", preferredStyle: UIAlertControllerStyle.alert)
            alert.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.default, handler: nil))
            self.present(alert, animated: true, completion: nil)
        } else {
            print("The event title is \((TitleTxt.text)!)")
            // this will perform the segue (of course the segue with the given identifier must exist)
            self.performSegue(withIdentifier: "CreateEvntBtn", sender: self)
        }
    }

    // this will give you the opportunity to configure your destination VC
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if (segue.identifier == "CreateEvntBtn") {
             let destVC = segue.destination as! CreatedEventController

             destVC.CrTitle = TitleTxt.text!
             destVC.CrCity = CityTxt.text!
             destVC.CrCountry = CountryTxt.text!
             destVC.CrVenue = VenueTxt.text!
             destVC.CrTime = TimeTxt.text!
             destVC.CrUrl = UrlTxt.text!
        }
    }
}

Answer 3

三期：

prepareForSegue 必须在 class 的顶层，而不是在另一个方法中。

prepareForSegue的签名有误。这是

func prepare(for segue: UIStoryboardSegue, sender: Any?) {

在 IBAction 你必须调用 performSegue(withIdentifier:sender)

else {
    print("The event title is \((TitleTxt.text)!)")
    performSegue(withIdentifier:"CreateEvntBtn", sender:nil)
}

如果您是 Swift 的新手，请习惯函数和变量名称以小写字母开头的命名约定。

Swift 3.0 标签变为空白（零值？）

Swift 3.0 Labels Coming Blank (Nil value?)

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swift

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