（Swift）PrepareForSegue：致命错误：在展开Optional值时意外发现nil [英] (Swift) PrepareForSegue: fatal error: unexpectedly found nil while unwrapping an Optional value

问题描述

DetailViewController：

  @IBOutlet var selectedBundesland：UILabel！ 
  

TableViewController：

 覆盖func prepareForSegue（segue：UIStoryboardSegue！，sender：AnyObject！）{
 
 
 if（segue.identifier ==BackToCalculator）{
 var vc ：FirstViewController = segue.destinationViewController as FirstViewController 
 vc.selectedBundesland.text =Test
} 
  

IBOutlet已连接！

错误：致命错误：在解包可选值时意外发现nil

<我读了很多关于Optionals的页面，但我不知道我的问题的答案。

您是否需要有关我的项目的更多信息？

解决方案

您不能直接写入中的 UILabel prepareForSegue 因为视图控制器尚未完全初始化。您需要创建另一个字符串属性来保存该值并将其放入相应函数的标签中 - 例如 viewWillAppear 。

DetailViewController:

    @IBOutlet var selectedBundesland: UILabel!

TableViewController:

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


    if (segue.identifier == "BackToCalculator") {
        var vc:FirstViewController = segue.destinationViewController as FirstViewController
            vc.selectedBundesland.text = "Test"
    }

IBOutlet is connected!

Error: fatal error: unexpectedly found nil while unwrapping an Optional value

I read multiple pages about Optionals but i didn't know the answer to my problem.

Do you need more information about my project?

解决方案

You cannot write directly to the UILabel in prepareForSegue because the view controller is not fully initialised yet. You need to create another string property to hold the value and put it into the label in the appropriate function - such as viewWillAppear.

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