标签中的Swift可选 [英] Swift optional in label

问题描述

我在这里有此代码

let fundsreceived = String(stringInterpolationSegment: self.campaign?["CurrentFunds"]!)
cell.FundsReceivedLabel.text = "$\(funds received)"

正在打印Optional(1000)

我已经将!添加到了变量中，但是可选选项并没有消失.知道我在这里做错了什么吗?

I have already added ! to the variable but the optional isn't going away. Any idea what have i done wrong here?

推荐答案

之所以发生这种情况，是因为您要传递给的参数

This is happening because the parameter you are passing to

String(stringInterpolationSegment:)

是可选.

是的，您做了force unwrap，但您仍然有Optional ...

Yes, you did a force unwrap and you still have an Optional...

如果您分解行，请保留...

Infact if you decompose your line...

let fundsreceived = String(stringInterpolationSegment: self.campaign?["CurrentFunds"]!)

转换为以下等效语句...

into the following equivalent statement...

let value = self.campaign?["CurrentFunds"]! // value is an Optional, this is the origin of your problem
let fundsreceived = String(stringInterpolationSegment: value)

您发现value是Optional！

1. 因为self.campaign? 产生和Optional
2. 然后["CurrentFunds"] 产生另一个Optional
3. 最后，你的部队unwrap 撤出一个Optional

1. Because self.campaign? produces an Optional
2. Then ["CurrentFunds"] produces another Optional
3. Finally your force unwrap removes one Optional

因此 2个可选- 1个可选 = 1个可选

首先是我能找到的最丑陋的解决方案

我正在编写此解决方案只是为了告诉您您应该不要做什么.

let fundsreceived = String(stringInterpolationSegment: self.campaign!["CurrentFunds"]!)

如您所见，我用强制展开!替换了您的条件展开?.只是不要在家做！

As you can see I replaced your conditional unwrapping ? with a force unwrapping !. Just do not do it at home!

请记住，您应该尽可能避免使用此人!！

Remember, you should avoid this guy ! everytime you can!

if let
    campaign = self.campaign,
    currentFunds = campaign["CurrentFunds"] {
        cell.FundsReceivedLabel.text = String(stringInterpolationSegment:currentFunds)
}

1. 在这里，我们使用conditional binding将可选的self.campaign转换为non optional常量(如果可能).
2. 然后我们将campaign["CurrentFunds"]的值转换为non optional type(如果可能).

1. Here we are using conditional binding to transform the optional self.campaign into a non optional constant (when possible).
2. Then we are transforming the value of campaign["CurrentFunds"] into a non optional type (when possible).

最后，如果IF成功，我们可以放心使用currentFunds，因为它不是可选的.

Finally, if the IF does succeed, we can safely use currentFunds because it is not optional.

希望这会有所帮助.

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