基于对象范例中可接受的答案

class ISO8601Format
{
    let format: ISO8601DateFormatter

    init() {
        let format = ISO8601DateFormatter()
        format.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
        format.timeZone = TimeZone(secondsFromGMT: 0)!
        self.format = format
    }

    func date(from string: String) -> Date {
        guard let date = format.date(from: string) else { fatalError() }
        return date
    }

    func string(from date: Date) -> String { return format.string(from: date) }
}


class ISO8601Time
{
    let date: Date
    let format = ISO8601Format() //FIXME: Duplication

    required init(date: Date) { self.date = date }

    convenience init(string: String) {
        let format = ISO8601Format() //FIXME: Duplication
        let date = format.date(from: string)
        self.init(date: date)
    }

    func concise() -> String { return format.string(from: date) }

    func description() -> String { return date.description(with: .current) }
}

callsite

let now = Date()
let time1 = ISO8601Time(date: now)
print("time1.concise(): \(time1.concise())")
print("time1: \(time1.description())")


let time2 = ISO8601Time(string: "2020-03-24T23:16:17.661Z")
print("time2.concise(): \(time2.concise())")
print("time2: \(time2.description())")

在我的情况下，我必须将DynamoDB - lastUpdated列(Unix时间戳)转换为正常时间。

lastUpdated的初始值是:1460650607601 -转换为2016-04-14 16:16:47 +0000通过:

   if let lastUpdated : String = userObject.lastUpdated {

                let epocTime = NSTimeInterval(lastUpdated)! / 1000 // convert it from milliseconds dividing it by 1000

                let unixTimestamp = NSDate(timeIntervalSince1970: epocTime) //convert unix timestamp to Date
                let dateFormatter = NSDateFormatter()
                dateFormatter.timeZone = NSTimeZone()
                dateFormatter.locale = NSLocale.currentLocale() // NSLocale(localeIdentifier: "en_US_POSIX")
                dateFormatter.dateFormat =  "yyyy-MM-dd'T'HH:mm:ssZZZZZ"
                dateFormatter.dateFromString(String(unixTimestamp))

                let updatedTimeStamp = unixTimestamp
                print(updatedTimeStamp)

            }

斯威夫特5

如果你的目标系统是iOS 11.0+ / macOS 10.13+，你只需使用带有withInternetDateTime和withFractionalSeconds选项的ISO8601DateFormatter，如下所示:

let date = Date()

let iso8601DateFormatter = ISO8601DateFormatter()
iso8601DateFormatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
let string = iso8601DateFormatter.string(from: date)

// string looks like "2020-03-04T21:39:02.112Z"

有一个新的ISO8601DateFormatter类，它允许您创建一个只有一行的字符串。为了向后兼容，我使用了一个旧的c库。我希望这对某些人有用。

斯威夫特3.0

extension Date {
    var iso8601: String {
        if #available(OSX 10.12, iOS 10.0, watchOS 3.0, tvOS 10.0, *) {
            return ISO8601DateFormatter.string(from: self, timeZone: TimeZone.current, formatOptions: .withInternetDateTime)
        } else {
            var buffer = [CChar](repeating: 0, count: 25)
            var time = time_t(self.timeIntervalSince1970)
            strftime_l(&buffer, buffer.count, "%FT%T%z", localtime(&time), nil)
            return String(cString: buffer)
        }
    }
}

为了补充Leo Dabus的版本，我增加了对Swift和Objective-C编写的项目的支持，也增加了对可选毫秒的支持，可能不是最好的，但你会明白的:

Xcode 8和Swift 3

extension Date {
    struct Formatter {
        static let iso8601: DateFormatter = {
            let formatter = DateFormatter()
            formatter.calendar = Calendar(identifier: .iso8601)
            formatter.locale = Locale(identifier: "en_US_POSIX")
            formatter.timeZone = TimeZone(secondsFromGMT: 0)
            formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSXXXXX"
            return formatter
        }()
    }

    var iso8601: String {
        return Formatter.iso8601.string(from: self)
    }
}


extension String {
    var dateFromISO8601: Date? {
        var data = self
        if self.range(of: ".") == nil {
            // Case where the string doesn't contain the optional milliseconds
            data = data.replacingOccurrences(of: "Z", with: ".000000Z")
        }
        return Date.Formatter.iso8601.date(from: data)
    }
}


extension NSString {
    var dateFromISO8601: Date? {
        return (self as String).dateFromISO8601
    }
}

请记住按照Technical Q&A1480中的描述将区域设置为en_US_POSIX。在Swift 3中:

let date = Date()
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZZZZZ"
print(formatter.string(from: date))

问题是，如果您在使用非公历的设备上，年份将不符合RFC3339/ISO8601，除非您指定区域设置以及timeZone和dateFormat字符串。

或者你可以使用ISO8601DateFormatter来让你自己摆脱设置locale和timeZone的麻烦:

let date = Date()
let formatter = ISO8601DateFormatter()
formatter.formatOptions.insert(.withFractionalSeconds)  // this is only available effective iOS 11 and macOS 10.13
print(formatter.string(from: date))

对于Swift 2的演绎，请参见此答案的先前修订。