至于swift 3，我必须强制我的#%@!字符串和int加上一个“!”否则它就不起作用。

例如:

let prefs = UserDefaults.standard
var counter: String!
counter = prefs.string(forKey:"counter")
print("counter: \(counter!)")


var counterInt = Int(counter!)
counterInt = counterInt! + 1
print("counterInt: \(counterInt!)")

OUTPUT:
counter: 1
counterInt: 2

你可以使用NSNumberFormatter(). numberfromstring (yourNumberString)。这很好，因为它返回一个可选的，然后你可以用if let测试，以确定转换是否成功。 如。

var myString = "\(10)"
if let myNumber = NSNumberFormatter().numberFromString(myString) {
    var myInt = myNumber.integerValue
    // do what you need to do with myInt
} else {
    // what ever error code you need to write
}

斯威夫特5

var myString = "\(10)"
if let myNumber = NumberFormatter().number(from: myString) {
    var myInt = myNumber.intValue
    // do what you need to do with myInt
  } else {
    // what ever error code you need to write
  }

转换字符串值为整数在Swift 4

let strValue:String = "100"
let intValue = strValue as! Int
var intValueFromString:Int = strValue as! Int
or
var intValueFromString = Int(strValue)!

@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
}

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

我已经做了一个简单的程序，其中有2个TXT字段，您从用户输入并添加它们，以使其更容易理解，请找到下面的代码。

@IBOutlet weak var result: UILabel!
@IBOutlet weak var one: UITextField!
@IBOutlet weak var two: UITextField!

@IBAction func add(sender: AnyObject) {        
    let count = Int(one.text!)
    let cal = Int(two.text!)
    let sum = count! + cal!
    result.text = "Sum is \(sum)"
}

希望这能有所帮助。