Question

我目前在destViewController.titleLabel.text =“Testing Segue”中打开一个致命错误时意外发现nil，同时解包一个可选值。

如何修复它，因为它在转到SecondViewController时遇到错误？我如何避免在titleLabel.text上获得nil？

class ViewController: UIViewController {

        @IBAction func action(sender: AnyObject) {

            let alertController: UIAlertController = UIAlertController (title: "Next Page", message: "", preferredStyle: .Alert)

            let yesAction = UIAlertAction (title: "YES", style: .Default ) { action -> Void in self.performSegueWithIdentifier("test", sender: self)
            }

            alertController.addAction (yesAction)

            self.presentViewController(alertController, animated: true, completion: nil)

        override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

            if (segue.identifier == "test") {

               let destViewController : SecondViewController = segue.destinationViewController as SecondViewController

                destViewController.titleLabel.text = "Testing Segue"

            }
        }
    }

Answer 1

首先，在您的ViewController中更新您的代码：

class ViewController: UIViewController {

@IBAction func action(sender: AnyObject) {

    let alertController: UIAlertController = UIAlertController (title: "Next Page", message: "", preferredStyle: .Alert)

    let yesAction = UIAlertAction (title: "YES", style: .Default ) { action -> Void in self.performSegueWithIdentifier("test", sender: self)
    }

    alertController.addAction (yesAction)

    self.presentViewController(alertController, animated: true, completion: nil)
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {

    if (segue.identifier == "test") {

        let destViewController : SecondViewController = segue.destinationViewController as SecondViewController

        destViewController.textlbl = "Testing Segue"

        }

    }
}

之后我认为你无法用你的方式为textLabel赋予价值，所以在你的SecondViewController中以这种方式为该标签赋值：

import UIKit

class SecondViewController: UIViewController {

@IBOutlet weak var titleLabel: UILabel!
var textlbl = String()
override func viewDidLoad() {
    super.viewDidLoad()

    self.titleLabel.text = textlbl
    }
}

HERE我为您提供了一个示例项目供您参考。

准备切换到查看控制器时发生致命错误

1 个答案: