Question

我需要一个来自全局范围的函数来更改故事板上的标签。

当我尝试运行此代码时，我得到的错误是：

fatal error: unexpectedly found nil while unwrapping an Optional value

问题是viewController.congratulations为null。

如何解决这个问题？提前谢谢！

func myAlert ()
{
    // how to change 'configuration.text' from here?

    let storyboard = UIStoryboard(name: "Main", bundle: nil);
    let viewController : ViewController = storyboard.instantiateViewController(withIdentifier: "ViewController") as! ViewController;

    viewController.congratulations.text = "test";
}

class ViewController: UIViewController
{
    @IBOutlet weak var congratulations: UILabel!;

    override func viewDidLoad()
    {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        myAlert();
    }

    override func didReceiveMemoryWarning()
    {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}

Answer 1

您不应直接尝试从定义它的类外部访问UILabel。只有在viewDidLoad子类的特定实例上调用UIViewController时才会创建标签。

您应该做的是将您想要在标签上显示的文字存储在另一个变量中，并在课堂外更改该变量。

Answer 2

名为congratulations的IBOutlet在viewDidLoad中为零。因此，在String（比如stringValue）创建一个ViewController属性。导航时设置该字符串属性

在viewController的viewDidLoad方法中，获取stringValue并将其值设置为label

self.congratulations.text = stringValue;

Answer 3

将myAlert（）添加到ViewController类中解决了这个问题。

class ViewController: UIViewController
{
    func myAlert ()
    {
        self.congratulations.text = "vrebreberbfrbb";
    }

    @IBOutlet weak var congratulations: UILabel!;

    override func viewDidLoad()
    {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        myAlert();
    }

    override func didReceiveMemoryWarning()
    {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}

如何从全局范围更改出口属性？

3 个答案: