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

问题描述

我正在尝试运行此代码，但我一直收到此错误：

I am trying to run this code but I keep on getting this error:

致命错误：在解包可选时意外发现nil价值

fatal error: unexpectedly found nil while unwrapping an Optional value

我不明白这意味着什么或为什么我得到它。任何提示？

I don't understand what it means or why I'm getting it. Any hint?

import UIKit

class ViewController: UIViewController {

var lastNumber: String = ""
@IBOutlet var answerField: UILabel
@IBOutlet var operaterLabel: UILabel

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

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

@IBAction func buttonTapped(theButton: UIButton) {
    if answerField.text == "0"
    {
        answerField.text = theButton.titleLabel.text
    }
    else
    {
        answerField.text = answerField.text + theButton.titleLabel.text
    }
}

@IBAction func plusTapped(theButton: UIButton) {
    // error is talking about the next line
    if operaterLabel.text == ""
    {
        operaterLabel.text = "+"
        lastNumber = answerField.text
        answerField.text = "0"
    }
    else
    {
        enterTapped(nil)
        operaterLabel.text = "+"
    }

}

@IBAction func minusTapped(theButton: UIButton) {
    if operaterLabel.text == ""
    {
        operaterLabel.text = "-"
        lastNumber = answerField.text
        answerField.text = "0"
    }
    else
    {
        enterTapped(nil)
        operaterLabel.text = "-"
    }

}

@IBAction func clearTapped(AnyObject) {
    answerField.text = "0"
    operaterLabel.text = ""
    lastNumber = ""

}

@IBAction func enterTapped(AnyObject?) {

    var num1 = lastNumber.toInt()
    var num2 = answerField.text.toInt()
    if !num1 || !num2
    {
        showError()
        return
    }
    var answer = 0
    if operaterLabel.text == "-"
    {
        var answer = num1! - num2!
    }
    else if operaterLabel.text == "+"
    {
        var answer = num1! + num2!
    }
    else
    {
        showError()
        return
    }
    answerField.text = "\(answer)"

}

func showError()
{
    println("Ther was an error")
}
}

推荐答案

错误是指您正在访问的参数可选值设置为nil时的可选值（例如，当 answerField 为nil时访问 answerField.text ），可能是您的两个 UILabels 。

the error refers to the fact that you're accessing the parameter of an optional value when the optional value is set to nil (e.g. accessing answerField.text when answerField is nil), likely one of your two UILabels.

如果行 operaterLabel.text ==抛出异常，那么 operaterLabel 是零。确认您已成功将其连接到Interface Builder文件中的标签。

If the line operaterLabel.text == "" is throwing the exception, then your operaterLabel is nil. Verify that you have connected it successfully to the label in your Interface Builder file.

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