if 语句或意外的 nil，同时解包错误；不确定哪个

Question

*快速说明，图片将有助于解释我的情况。所以目前，我只是添加了精液。学分和 GPA 文本字段到我的 GPA 计算器应用程序。这两个字段是可选的，而下面的其他 4 个字段不是。这是我的大部分代码（请原谅目前的冗余）。

         if CumCredits == "" || CumGPA == ""
        {
            let credit1 = Float(Credits1TF.text!)!
            let credit2 = Float(Credits2TF.text!)!

            let grade1 = Float(Grade1TF.text!)!
            let grade2 = Float(Grade2TF.text!)!

            let firstgrade = credit1 * grade1
            let secondgrade = credit2 * grade2

            let allcredits = credit1 + credit2
            let allgrades = firstgrade + secondgrade

            let finalgrade = round((allgrades / allcredits) * 10000)/10000


            GPALabel.text = "Your Semester GPA is: \(finalgrade)"
            GPALabel.hidden = false

            Class1TF.resignFirstResponder()
            Class2TF.resignFirstResponder()
            Credits1TF.resignFirstResponder()
            Credits2TF.resignFirstResponder()
            Grade1TF.resignFirstResponder()
            Grade2TF.resignFirstResponder()


            }
            else {
            let credit1 = Float(Credits1TF.text!)!
            let credit2 = Float(Credits2TF.text!)!

            let grade1 = Float(Grade1TF.text!)!
            let grade2 = Float(Grade2TF.text!)!

            let firstgrade = credit1 * grade1
            let secondgrade = credit2 * grade2

            let allcredits = credit1 + credit2
            let allgrades = firstgrade + secondgrade

            let finalgrade = round((allgrades / allcredits) * 10000)/10000

            Class1TF.resignFirstResponder()
            Class2TF.resignFirstResponder()
            Credits1TF.resignFirstResponder()
            Credits2TF.resignFirstResponder()
            Grade1TF.resignFirstResponder()
            Grade2TF.resignFirstResponder()
            CumCredits.resignFirstResponder()
            CumGPA.resignFirstResponder()

            let CCredits = Float(CumCredits.text!)!
            let CGPA = Float(CumGPA.text!)!

            //top math
            let LastGrade = CCredits * CGPA
            let MegaCredits = allcredits + CCredits
            let MegaGPA = allgrades + LastGrade
            let MegaEverything = (round((MegaGPA / MegaCredits) * 10000)/10000) - 0.0001

            CumTotal.hidden = false
            CumTotal.text = "Your expected cumulative GPA is: \(MegaEverything)"
            GPALabel.text = "Your Semester GPA is: \(finalgrade)"
            GPALabel.hidden = false

            Class1TF.resignFirstResponder()
            Class2TF.resignFirstResponder()
            Credits1TF.resignFirstResponder()
            Credits2TF.resignFirstResponder()
            Grade1TF.resignFirstResponder()
            Grade2TF.resignFirstResponder()
            CumCredits.resignFirstResponder()
            CumGPA.resignFirstResponder()

        }

此刻（据我所知），如果暨。 Credits和GPA不用管，执行my语句的top部分，如果不为空则执行else语句。

所以我的问题...如果我为每个字段输入一个值，那么所有内容都没有问题。但是，如果我离开 Cum。学分或 GPA 字段为空，我的程序崩溃，我得到典型的 "unexpectedly found nil while unwrapping an Optional value" 处理

 let CCredits = Float(CumCredits.text!)!
 let CGPA = Float(CumGPA.text!)!

我已经尝试了很多可能的解决方案：重写代码和重新措辞代码，但我似乎无法理解。你能提出什么建议？

如有任何帮助，我们将不胜感激！

Answer 1

尝试强制解包可选时会发生此错误，因此请先查看每个“！”使用过，你可能会发现其中一个是零。

编辑在查看并讨论评论后，您的 if 语句似乎应该是

!CumCredits.characters.isEmpty || !CumGPA.characters.isEmpty

在这种情况下可能发生的情况是您的字段中的值为空字符串，因此尝试从条目字符串创建浮点数将导致 nil 值。

一个解决方案是在函数顶部放置一个 guard 语句，这样导致错误的代码永远不会是运行:

guard let credits1Text = Credits1TF.text, 
          credits2Text = Credits2TF.text, 
          grade1Text = Grade1TF.text, 
          grade2Text = Grad2TF.text
where !credits1Text.characters.isEmpty && !credits2Text.characters.isEmpty 
     && !grade1Text.characters.isEmpty && !grade2Text.characters.isEmpty else {
   *handle case where float conversion won't work*
}
*continue on with normal code, using verified values created in guard*

Answer 2

问题出在 if - 语句上。

I should have had CumCredits.text == "" || CumGPA.text == ""

这样一来，如果我的文本字段为空，它们将跳过我代码的第一部分。

if 语句或意外的 nil，同时解包错误；不确定哪个

if statement or unexpected nil while unwrapping error; unsure of which

textbox

if-statement

optional

ios

swift