如何检查零值？应用程序崩溃，即使考虑了零值。Swift[副本]

Question

我在Xcode上创建了一个简单的猜测游戏，用户必须正确猜测数字（0到5之间）。我以为我已经检查了我的textFieldInt的nil值，以确保如果没有提交值，应用程序不会崩溃。不幸的是，情况似乎并非如此，我也不确定我的错在哪里。

如果我没有输入值并按下按钮，我会收到以下错误消息：

致命错误：在展开可选值时意外发现nil

我以前遇到过这个问题，并通过正确检查nil的右选项来解决它。尽管现在它似乎仍然“意外地发现了nil”，即使已经考虑了nil值。

@IBOutlet var textField: UITextField!

@IBOutlet var label: UILabel!

@IBAction func buttonTapped(_ sender: Any) {
    let textFieldInt: UInt32 = UInt32(textField.text!)!
    let number = arc4random_uniform(6)

    if textFieldInt != nil {
        if textFieldInt != number {
            label.text = "Wrong! It was \(number)"
        }
        else if textFieldInt == number {
            label.text = "You're right!"
        }

    else {
        label.text = "Please enter a number!"
    }
}
}

Answer 1

使用if let或guard let测试您的值。例如

if let textFieldInt = UInt32(textField.text!)  {
    //textField.text! can be converted to UInt32
    if textFieldInt != number {
        label.text = "Wrong! It was \(number)"
    }
    else if textFieldInt == number {
        label.text = "You're right!"
    }
}else {
    //textField.text! can NOT be converted to UInt32
    label.text = "Please enter a number!"
}

或者

guard let textFieldInt = UInt32(textField.text!) else {
    //textField.text! can NOT be converted to UInt32
    label.text = "Please enter a number!"
    return
}
//textField.text! can be converted to UInt32
if textFieldInt != number {
    label.text = "Wrong! It was \(number)"
}
else if textFieldInt == number {
    label.text = "You're right!"
}

Answer 2

我相信错误发生在

let textFieldInt: UInt32 = UInt32(textField.text!)!

如果textField为空，则textField。文本将为零，textField。短信 将导致崩溃。

你可以用like

        @IBAction func buttonTapped(_ sender: Any) {
            if textField.text != nil {
         let textFieldInt: UInt32 = UInt32(textField.text!)!
            let number = arc4random_uniform(6)

            if textFieldInt != nil {
                if textFieldInt != number {
                    label.text = "Wrong! It was \(number)"
                }
                else if textFieldInt == number {
                    label.text = "You're right!"
                }

            else {
                label.text = "Please enter a number!"
            }
        }
      }
              else {
              label.text = "Please enter a number!"
        }
  }