//  To convert user input (i.e string) to int for calculation.I did this , and it works.


    let num:Int? = Int(firstTextField.text!);

    let sum:Int = num!-2

    print(sum);

我最近也遇到了同样的问题。下面的解决方案对我来说是可行的:

        let strValue = "123"
        let result = (strValue as NSString).integerValue

有用的字符串到Int和其他类型

extension String {
        //Converts String to Int
        public func toInt() -> Int? {
            if let num = NumberFormatter().number(from: self) {
                return num.intValue
            } else {
                return nil
            }
        }

        //Converts String to Double
        public func toDouble() -> Double? {
            if let num = NumberFormatter().number(from: self) {
                return num.doubleValue
            } else {
                return nil
            }
        }

        /// EZSE: Converts String to Float
        public func toFloat() -> Float? {
            if let num = NumberFormatter().number(from: self) {
                return num.floatValue
            } else {
                return nil
            }
        }

        //Converts String to Bool
        public func toBool() -> Bool? {
            return (self as NSString).boolValue
        }
    }

像这样使用它:

"123".toInt() // 123

@IBAction func calculateAclr(_ sender: Any) {
    if let addition = addition(arrayString: [txtBox1.text, txtBox2.text, txtBox3.text]) {
      print("Answer = \(addition)")
      lblAnswer.text = "\(addition)"
    }
}

func addition(arrayString: [Any?]) -> Int? {

    var answer:Int?
    for arrayElement in arrayString {
        if let stringValue = arrayElement, let intValue = Int(stringValue)  {
            answer = (answer ?? 0) + intValue
        }
    }

    return answer
}

我的解决方案是有一个一般的扩展字符串到int转换。

extension String {

 // default: it is a number suitable for your project if the string is not an integer

    func toInt(default: Int) -> Int {
        if let result = Int(self) {
            return result
        }
        else {
            return default  
        }
    }

}

用这个:

// get the values from text boxes
    let a:Double = firstText.text.bridgeToObjectiveC().doubleValue
    let b:Double = secondText.text.bridgeToObjectiveC().doubleValue

//  we checking against 0.0, because above function return 0.0 if it gets failed to convert
    if (a != 0.0) && (b != 0.0) {
        var ans = a + b
        answerLabel.text = "Answer is \(ans)"
    } else {
        answerLabel.text = "Input values are not numberic"
    }

OR

使你的UITextField KeyboardType为DecimalTab从你的XIB或故事板，并删除任何if条件做任何计算，即。

var ans = a + b
answerLabel.text = "Answer is \(ans)"

因为键盘类型是DecimalPad，没有机会输入其他0-9或。

希望这对你有帮助!!