How can I parse create a date time stamp formatted with fractional seconds UTC timezone ISO 8601 RFC 3339 in Swift

Question

How to generate a date time stamp  using the format standards for ISO 8601 and RFC 3339   The goal is a string that looks like this    2015-01-01T00 00 00 000Z    Format    year  month  day  as  XXXX-XX-XX  the letter  T  as a separator hour  minute  seconds  milliseconds  as  XX XX XX XXX   the letter  Z  as a zone designator for zero offset  a k a  UTC  GMT  Zulu time    Best case    Swift source code that is simple  short  and straightforward  No need to use any additional framework  subproject  cocoapod  C code  etc    I ve searched StackOverflow  Google  Apple  etc  and haven t found a Swift answer to this    The classes that seem most promising are NSDate  NSDateFormatter  NSTimeZone   Related Q amp A  How do I get ISO 8601 date in iOS   Here s the best I ve come up with so far   var now   NSDate   var formatter   NSDateFormatter   formatter dateFormat    yyyy-MM-dd T HH mm ss SSS Z   formatter timeZone   NSTimeZone forSecondsFromGMT  0  println formatter stringFromDate now

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If you want to use the ISO8601DateFormatter   with a date from a Rails 4  JSON feed  and don t need millis of course   you need to set a few options on the formatter for it to work right otherwise the the date from  string  function will return nil  Here s what I m using   extension Date       init dateString String            self   Date iso8601Formatter date from  dateString              static let iso8601Formatter  ISO8601DateFormatter             let formatter   ISO8601DateFormatter           formatter formatOptions     withFullDate                                             withTime                                             withDashSeparatorInDate                                             withColonSeparatorInTime          return formatter             Here s the result of using the options verses not in a playground screenshot

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Uses ISO8601DateFormatter on iOS10 or newer   Uses DateFormatter on iOS9 or older   Swift 4  protocol DateFormatterProtocol       func string from date  Date  - gt  String     func date from string  String  - gt  Date     extension DateFormatter  DateFormatterProtocol      available iOS 10 0     extension ISO8601DateFormatter  DateFormatterProtocol     struct DateFormatterShared       static let iso8601  DateFormatterProtocol             if  available iOS 10                   return ISO8601DateFormatter             else                  iOS 9             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

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In the future the format might need to be changed which could be a small head ache having date dateFromISO8601 calls everywhere in an app   Use a class and protocol to wrap the implementation  changing the date time format call in one place will be simpler   Use RFC3339 if possible  its a more complete representation   DateFormatProtocol and DateFormat is great for  dependency injection   class AppDelegate  UIResponder  UIApplicationDelegate        internal static let rfc3339DateFormat    yyyy-MM-dd T HH mm ssZZZZZ      internal static let localeEnUsPosix    en US POSIX     import Foundation  protocol DateFormatProtocol        func format date  NSDate  - gt  String     func parse date  String  - gt  NSDate       import Foundation  class DateFormat   DateFormatProtocol        func format date  NSDate  - gt  String           return date rfc3339            func parse date  String  - gt  NSDate            return date rfc3339            extension NSDate        struct Formatter           static let rfc3339  NSDateFormatter                 let formatter   NSDateFormatter               formatter calendar   NSCalendar calendarIdentifier  NSCalendarIdentifierISO8601              formatter locale   NSLocale localeIdentifier  AppDelegate localeEnUsPosix              formatter timeZone   NSTimeZone forSecondsFromGMT  0              formatter dateFormat   rfc3339DateFormat             return formatter                        var rfc3339  String   return Formatter rfc3339 stringFromDate self       extension String       var rfc3339  NSDate            return NSDate Formatter rfc3339 dateFromString self             class DependencyService  DependencyServiceProtocol        private var dateFormat  DateFormatProtocol       func setDateFormat dateFormat  DateFormatProtocol            self dateFormat   dateFormat            func getDateFormat   - gt  DateFormatProtocol           if let dateFormatObject   dateFormat                return dateFormatObject           else               let dateFormatObject   DateFormat               dateFormat   dateFormatObject              return dateFormatObject

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Without some manual String masks or TimeFormatters   import Foundation  struct DateISO  Codable       var date  Date    extension Date      var isoString  String           let encoder   JSONEncoder           encoder dateEncodingStrategy    iso8601         guard let data   try  encoder encode DateISO date  self            let json   try  JSONSerialization jsonObject with  data  options   allowFragments  as    String  String              else   return              return json  first  value                let dateString   Date   isoString

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Swift 4     iOS 11 2 1 or later extension ISO8601DateFormatter       convenience init   formatOptions  Options            self init           self formatOptions   formatOptions           extension Formatter       static let iso8601withFractionalSeconds   ISO8601DateFormatter   withInternetDateTime   withFractionalSeconds       extension Date       var iso8601withFractionalSeconds  String   return Formatter iso8601withFractionalSeconds string from  self        extension String       var iso8601withFractionalSeconds  Date    return Formatter iso8601withFractionalSeconds date from  self        Usage  Date   description with   current       Tuesday  February 5  2019 at 10 35 01 PM Brasilia Summer Time quot  let dateString   Date   iso8601withFractionalSeconds        quot 2019-02-06T00 35 01 746Z quot   if let date   dateString iso8601withFractionalSeconds       date description with   current      quot Tuesday  February 5  2019 at 10 35 01 PM Brasilia Summer Time quot      print date iso8601withFractionalSeconds                 quot 2019-02-06T00 35 01 746Z n quot      iOS 9     Swift 3 or later extension Formatter       static let iso8601withFractionalSeconds  DateFormatter             let formatter   DateFormatter           formatter calendar   Calendar identifier   iso8601          formatter locale   Locale identifier   quot en US POSIX quot           formatter timeZone   TimeZone secondsFromGMT  0          formatter dateFormat    quot yyyy-MM-dd T HH mm ss SSSXXXXX quot          return formatter              Codable Protocol If you need to encode and decode this format when working with Codable protocol you can create your own custom date encoding decoding strategies   extension JSONDecoder DateDecodingStrategy       static let iso8601withFractionalSeconds   custom           let container   try  0 singleValueContainer           let string   try container decode String self          guard let date   Formatter iso8601withFractionalSeconds date from  string  else               throw DecodingError dataCorruptedError in  container                    debugDescription   quot Invalid date   quot    string                    return date          and the encoding strategy extension JSONEncoder DateEncodingStrategy       static let iso8601withFractionalSeconds   custom           var container    1 singleValueContainer           try container encode Formatter iso8601withFractionalSeconds string from   0             Playground Testing let dates    Date           quot Feb 8  2019 at 9 48 PM quot    encoding let encoder   JSONEncoder   encoder dateEncodingStrategy    iso8601withFractionalSeconds let data   try  encoder encode dates  print String data  data  encoding   utf8     decoding let decoder   JSONDecoder   decoder dateDecodingStrategy    iso8601withFractionalSeconds let decodedDates   try  decoder decode  Date  self  from  data        quot Feb 8  2019 at 9 48 PM quot

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To complement the version of Leo Dabus  I added support for projects written Swift and Objective-C  also added support for the optional milliseconds  probably isn t the best but you would get the point   Xcode 8 and 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

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Remember to set the locale to en US POSIX as described in Technical Q amp A1480  In Swift 3   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     The issue is that if you re on a device which is using a non-Gregorian calendar  the year will not conform to RFC3339 ISO8601 unless you specify the locale as well as the timeZone and dateFormat string   Or you can use ISO8601DateFormatter to get you out of the weeds of setting locale and timeZone yourself   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     For Swift 2 rendition  see previous revision of this answer

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To further compliment Andr  s Torres Marroqu  n and Leo Dabus  I have a version that preserves fractional seconds  I can t find it documented anywhere  but Apple truncate fractional seconds to the microsecond  3 digits of precision  on both input and output  even though specified using SSSSSSS  contrary to Unicode tr35-31    I should stress that this is probably not necessary for most use cases  Dates online do not typically need millisecond precision  and when they do  it is often better to use a different data format  But sometimes one must interoperate with a pre-existing system in a particular way   Xcode 8 9 and Swift 3 0-3 2  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 identifier   UTC               formatter dateFormat    yyyy-MM-dd T HH mm ss SSSSSSXXXXX              return formatter                        var iso8601  String              create base Date format           var formatted   DateFormatter iso8601 string from  self              Apple returns millisecond precision  find the range of the decimal portion          if let fractionStart   formatted range of                     let fractionEnd   formatted index fractionStart lowerBound  offsetBy  7  limitedBy  formatted endIndex                 let fractionRange   fractionStart lowerBound   lt fractionEnd                replace the decimal range with our own 6 digit fraction output              let microseconds   self timeIntervalSince1970 - floor self timeIntervalSince1970               var microsecondsStr   String format     06f   microseconds               microsecondsStr remove at  microsecondsStr startIndex               formatted replaceSubrange fractionRange  with  microsecondsStr                     return formatted          extension String       var dateFromISO8601  Date            guard let parsedDate   Date Formatter iso8601 date from  self  else               return nil                    var preliminaryDate   Date timeIntervalSinceReferenceDate  floor parsedDate timeIntervalSinceReferenceDate            if let fractionStart   self range of                    let fractionEnd   self index fractionStart lowerBound  offsetBy  7  limitedBy  self endIndex                let fractionRange   fractionStart lowerBound   lt fractionEnd             let fractionStr   self substring with  fractionRange               if var fraction   Double fractionStr                    fraction   Double floor 1000000 fraction  1000000                  preliminaryDate addTimeInterval fraction                                  return preliminaryDate

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There is a new ISO8601DateFormatter class that let s you create a string with just one line  For backwards compatibility I used an old C-library  I hope this is useful for someone   Swift 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  amp buffer  buffer count    FT T z   localtime  amp time   nil              return String cString  buffer

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Swift 5  If you re targeting iOS 11 0    macOS 10 13   you simply use ISO8601DateFormatter with the withInternetDateTime and withFractionalSeconds options  like so   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

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Based on the acceptable answer in an object paradigm  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  - gt  Date           guard let date   format date from  string  else   fatalError             return date            func string from date  Date  - gt  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   - gt  String   return format string from  date         func description   - gt  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

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In my case I have to convert the DynamoDB - lastUpdated column  Unix Timestamp  to Normal Time    The initial value of lastUpdated was    1460650607601 - converted down to 2016-04-14 16 16 47  0000 via        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

[date] How can I parse / create a date time stamp formatted with fractional seconds UTC timezone (ISO 8601, RFC 3339) in Swift?

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