"可选类型'String的值？没有包装;你是说用'！'要么 '？' ？” [英] "Value of optional type 'String?' not unwrapped; did you mean to use '!' or '?' ?"

问题描述

我已经很长时间没有研究iOS或Swift了。借助最新的Xcode更新之一，我在计算机上制作的许多应用现在似乎都在使用过时的语法。

I have not been studying iOS or Swift for very long. With one of the latest Xcode updates, many of the apps I have made on my computer now appear to be using obsolete syntax.

Xcode通过将其转换为新语法来与我们对话但通常无法解决任何问题，而我又遇到了新问题。这是语法转换后我制作的第一个应用程序的代码。我收到一条错误消息：

Xcode talks us through converting it to new syntax but often that does not solve anything and I have a new problem. Here is code for one of the first app I made after the syntax has been converted. I am getting an error saying:

可选类型字符串？的值未包装；您是要使用
'！'还是'？'吗？

Value of optional type 'String?' not unwrapped; did you mean to use '!' or '?' ?

我知道这一定很简单，但我不知道不知道如何解决。这是我的代码：

I know this must be really simple but I don't know how to fix it. Here is my code:

@IBAction func findAge(sender: AnyObject) {
    var enteredAge = Int(age.text)
    if enteredAge != nil {
        var catYears = enteredAge! * 7
        resultLabel.text = "Your cat is \(catYears) in cat years"
    } else {
        resultLabel.text = "Please enter a whole number"
    }
}  

推荐答案

text 属性是可选的，使用前必须先将其打开。

The text property of a text label is an optional, you have to unwrap it before using it.

var enteredAge = Int(age.text!)

甚至更好：

if let text = age.text, let enteredAge = Int(text) {
    let catYears = enteredAge * 7
    resultLabel.text = "Your cat is \(catYears) in cat years"
} else {
    resultLabel.text = "Please enter a whole number"
}

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