在雨燕3中，

NumberFormatter.localizedString(from: NSNumber(value: whatever), number: NumberFormatter.Style.decimal)

Swift Xcode 6.3，SOLVED（我决定在代码中保留$）。如果您不希望在输出中出现$，请将.CurrencyStyle更改为.DecimalStyle

var fv = 3534234.55 
var formatter = NSNumberFormatter()
formatter.numberStyle = .CurrencyStyle
formatter.maximumFractionDigits = 0;
resultFV.text = formatter.stringFromNumber(fv) // result: $3,534,235 –

为此，您应该使用NumberFormatter：

let numberFormatter = NumberFormatter()
numberFormatter.numberStyle = .decimal

resultFV.text = numberFormatter.string(from: fv)

Swift 4.1货币字符串更新：

let balance = 1234567

let formatter = NumberFormatter()
formatter.numberStyle = .currency
formatter.maximumFractionDigits = 0

let result = formatter.string(from: NSNumber(value: balance)) 
// result: $1,234,567

您可以将formatter.numberStyle更改为.decimal，使其保留为不带“$”符号的数字。

你可以通过使用Swift 3+中的String初始化器来实现这一点：

// 1605436
let value: Int = 1605436

// "1,605,436" where Locale == en_US
let formattedInt = String(format: "%d", locale: Locale.current, value) 

// "1,605,436" where Locale == en_US
let formattedDouble = String(format: "%.0f", locale: Locale.current, Double(value))

Swift 5的更新

var unformattedValue : Double = 3534234.55
var formatter = NumberFormatter()
formatter.numberStyle = .currency // or .decimal if desired
formatter.maximumFractionDigits = 2; //change as desired
formatter.locale = Locale.current // or = Locale(identifier: "de_DE"), more locale identifier codes: https://gist.github.com/jacobbubu/1836273
var displayValue : String = formatter.string(from: NSNumber(value: unformattedValue))! // displayValue: "$3,534,235" ```

为什么不限制精度，比如".0f"

resultFV.text = String.localizedStringWithFormat("%.0f", fv)

更新答案：

var formatter: NSNumberFormatter = NSNumberFormatter()
formatter.numberStyle = NSNumberFormatterStyle.DecimalStyle;
var formattedStr: NSString = formatter.stringFromNumber(NSNumber(double: fv))!
resultFV.text = formattedStr

更新
使用Foundation中适用于macOS 12.0+、iOS 15.0+、tvOS 15.0+和watchOS 8.0+的数据格式。

let number: Int = 1000  
  let formatted = number.formatted(.number.grouping(.never))  
  print(formatted)

控制台输出："1000"
number可以是任何BinaryFloatingPoint或BinaryInteger