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

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问题描述

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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