Date to milliseconds and back to date in Swift

Question

I am taking the current time  in UTC  and putting it in nanaoseconds and then I need to take the nanoseconds and go back to a date in local time  I am able to do get the time to nanoseconds and then back to a date string but the time gets convoluted when I go from a string to date         Date to milliseconds      func currentTimeInMiliseconds   - gt  Int                let currentDate   NSDate               let dateFormatter   DateFormatter               dateFormatter dateFormat   format             dateFormatter timeZone   NSTimeZone name   UTC   as TimeZone              let date   dateFormatter date from  dateFormatter string from  currentDate as Date               let nowDouble   date  timeIntervalSince1970             return Int nowDouble 1000                   Milliseconds to date     extension Int           func dateFromMilliseconds format String  - gt  Date               let date   NSDate    NSDate timeIntervalSince1970 Double self    1000 0              let dateFormatter   DateFormatter               dateFormatter dateFormat   format             dateFormatter timeZone   TimeZone current             let timeStamp   dateFormatter string from  date as Date   let formatter   DateFormatter               formatter dateFormat   format             return   formatter date  from  timeStamp                          The timestamp is correct but the date returned isn t

User · Answer

Prashant Tukadiya answer works  But if you want to save the value in UserDefaults and then compare it to other date you get yout int64 truncated so it can cause problems  I found a solution   Swift 4   You can save int64 as string in UserDefaults   let value  String Date   millisecondsSince1970  let stringValue   String value  UserDefaults standard set stringValue  forKey   int64String     Like that you avoid Int truncation   And then you can recover the original value   let int64String   UserDefaults standard string forKey   int64String   let originalValue   Int64 int64String     This allow you to compare it with other date values   let currentTime   Date   millisecondsSince1970 let int64String   UserDefaults standard string forKey   int64String   let originalValue   Int64 int64String      0   if currentTime  lt  originalValue        return false   else        return true     Hope this helps someone who has same problem

User · Answer

Unless you absolutely have to convert the date to an integer  consider using a Double instead to represent the time interval  After all  this is the type that timeIntervalSince1970 returns  All of the answers that convert to integers loose sub-millisecond precision  but this solution is much more accurate  although you will still lose some precision due to floating-point imprecision   public extension Date                The interval  in milliseconds  between the date value and         00 00 00 UTC on 1 January 1970          Equivalent to  self timeIntervalSince1970   1000       var millisecondsSince1970  Double           return self timeIntervalSince1970   1000                     Creates a date value initialized relative to 00 00 00 UTC      on 1 January 1970 by a given number of   milliseconds               equivalent to               self init timeIntervalSince1970  TimeInterval milliseconds    1000                - Parameter millisecondsSince1970  A time interval in milliseconds              init millisecondsSince1970  Double            self init timeIntervalSince1970  TimeInterval milliseconds    1000

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As  Travis Solution works but in some cases   var millisecondsSince1970 Int  WILL CAUSE CRASH APPLICATION     with error     Double value cannot be converted to Int because the result would be greater than Int max if it occurs Please update your answer with Int64    Here is Updated Answer   extension Date    var millisecondsSince1970 Int64           return Int64  self timeIntervalSince1970   1000 0  rounded               RESOLVED CRASH HERE            init milliseconds Int            self   Date timeIntervalSince1970  TimeInterval milliseconds   1000               About Int definitions      On 32-bit platforms  Int is the same size as Int32  and on 64-bit platforms  Int is the same size as Int64    Generally  I encounter this problem in iPhone 5  which runs in 32-bit env  New devices run 64-bit env now  Their Int will be Int64   Hope it is helpful to someone who also has same problem

User · Answer

Date to milliseconds func currentTimeInMiliseconds   - gt  Int       let currentDate   Date       let since1970   currentDate timeIntervalSince1970     return Int since1970   1000       Milliseconds to date extension Int       func dateFromMilliseconds   - gt  Date           return Date timeIntervalSince1970  TimeInterval self  1000            I removed seemingly useless conversion via string and all those random

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let dateTimeStamp   NSDate timeIntervalSince1970 Double currentTimeInMiliseconds    1000     UTC time    YOUR currentTimeInMiliseconds METHOD let dateFormatter   NSDateFormatter   dateFormatter timeZone   NSTimeZone localTimeZone    dateFormatter dateFormat    yyyy-MM-dd  dateFormatter dateStyle   NSDateFormatterStyle FullStyle dateFormatter timeStyle   NSDateFormatterStyle ShortStyle   let strDateSelect   dateFormatter stringFromDate dateTimeStamp  print  Local Time   strDateSelect    Local time   let dateFormatter2   NSDateFormatter   dateFormatter2 timeZone   NSTimeZone name   UTC   as NSTimeZone  dateFormatter2 dateFormat    yyyy-MM-dd   let date3   dateFormatter dateFromString strDateSelect  print  DATE  date3

User · Answer

Watch out if you are going to compare dates after the conversion   For instance  I got simulator s asset with date as TimeInterval 366144731 9   converted to milliseconds Int64 1344451931900  and back to TimeInterval 366144731 9000001   using   func convertToMilli timeIntervalSince1970  TimeInterval  - gt  Int64       return Int64 timeIntervalSince1970   1000     func convertMilliToDate milliseconds  Int64  - gt  Date       return Date timeIntervalSince1970   TimeInterval milliseconds    1000       I tried to fetch the asset by creationDate and it doesn t find the asset  as you could figure  the numbers are not the same   I tried multiple solutions to reduce double s decimal precision  like round interval 1000  1000  use NSDecimalNumber  etc    with no success   I ended up fetching by interval -1  lt  creationDate  lt  interval   1  instead of creationDate    Interval   There may be a better solution

User · Answer

I don t understand why you re doing anything with strings     extension Date       var millisecondsSince1970 Int64           return Int64  self timeIntervalSince1970   1000 0  rounded               init milliseconds Int64            self   Date timeIntervalSince1970  TimeInterval milliseconds    1000            Date   millisecondsSince1970    1476889390939 Date milliseconds  0      Dec 31  1969  4 00 PM   PDT variant of 1970 UTC

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Travis solution is right  but it loses milliseconds when a Date is generated  I have added a line to include the milliseconds into the date   If you don t need this precision  use the Travis solution because it will be faster   extension Date        func toMillis   - gt  Int64            return Int64 self timeIntervalSince1970   1000             init millis  Int64            self   Date timeIntervalSince1970  TimeInterval millis   1000           self addTimeInterval TimeInterval Double millis   1000    1000

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Heres a simple solution in Swift 5 iOS 13  extension Date            func toMilliseconds   - gt  Int64           Int64 self timeIntervalSince1970   1000             init milliseconds Int            self   Date   advanced by  TimeInterval integerLiteral  Int64 milliseconds   1000             This however assumes you have calculated the difference between UTF time and local time and adjusted and accounted for in the milliseconds  For that look to calendar var cal   Calendar current cal timeZone   TimeZone abbreviation   quot UTC quot    let difference   cal compare dateGiven  to  date  toGranularity   nanosecond

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