How do you create a Swift Date object

Question

How do you create a date object from a date in swift xcode   eg in javascript you would do      var day   new Date  2014-05-20

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Here s how I did it in Swift 4 2   extension Date            Create a date from specified parameters                 - Parameters            - year  The desired year           - month  The desired month           - day  The desired day         - Returns  A  Date  object     static func from year  Int  month  Int  day  Int  - gt  Date            let calendar   Calendar identifier   gregorian          var dateComponents   DateComponents           dateComponents year   year         dateComponents month   month         dateComponents day   day         return calendar date from  dateComponents     nil           Usage   let marsOpportunityLaunchDate   Date from year  2003  month  07  day  07

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Personally I think it should be a failable initialiser   extension Date        init  dateString  String            let dateStringFormatter   DateFormatter           dateStringFormatter dateFormat    yyyy-MM-dd          if let d   dateStringFormatter date from  dateString                self init timeInterval  0  since  d            else               return nil                     Otherwise a string with an invalid format will raise an exception

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Swift has its own Date type  No need to use NSDate  Creating a Date and Time in Swift In Swift  dates and times are stored in a 64-bit floating point number measuring the number of seconds since the reference date of January 1  2001 at 00 00 00 UTC  This is expressed in the Date structure  The following would give you the current date and time  let currentDateTime   Date    For creating other date-times  you can use one of the following methods  Method 1 If you know the number of seconds before or after the 2001 reference date  you can use that  let someDateTime   Date timeIntervalSinceReferenceDate  -123456789 0     Feb 2  1997  10 26 AM  Method 2 Of course  it would be easier to use things like years  months  days and hours  rather than relative seconds  to make a Date  For this you can use DateComponents to specify the components and then Calendar to create the date  The Calendar gives the Date context  Otherwise  how would it know what time zone or calendar to express it in     Specify date components var dateComponents   DateComponents   dateComponents year   1980 dateComponents month   7 dateComponents day   11 dateComponents timeZone   TimeZone abbreviation   quot JST quot      Japan Standard Time dateComponents hour   8 dateComponents minute   34     Create date from components let userCalendar   Calendar identifier   gregorian     since the components above  like year 1980  are for Gregorian let someDateTime   userCalendar date from  dateComponents   Other time zone abbreviations can be found here  If you leave that blank  then the default is to use the user s time zone  Method 3 The most succinct way  but not necessarily the best  could be to use DateFormatter  let formatter   DateFormatter   formatter dateFormat    quot yyyy MM dd HH mm quot  let someDateTime   formatter date from   quot 2016 10 08 22 31 quot    The Unicode technical standards show other formats that DateFormatter supports  Notes See my full answer for how to display the date and time in a readable format  Also read these excellent articles   How to work with dates and times in Swift 3  part 1  Dates  Calendars  and DateComponents How to work with dates and times in Swift 3  part 2  DateFormatter How to work with dates and times in Swift 3  part 3  Date arithmetic

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This is best done using an extension to the existing NSDate class   The following extension adds a new initializer which will create a date in the current locale using the date string in the format you specified   extension NSDate       convenience       init dateString String          let dateStringFormatter   NSDateFormatter         dateStringFormatter dateFormat    yyyy-MM-dd        dateStringFormatter locale   NSLocale localeIdentifier   en US POSIX         let d   dateStringFormatter dateFromString dateString         self init timeInterval 0  sinceDate d             Now you can create an NSDate from Swift just by doing   NSDate dateString  2014-06-06     Please note that this implementation does not cache the NSDateFormatter  which you might want to do for performance reasons if you expect to be creating many NSDates in this way   Please also note that this implementation will simply crash if you try to initialize an NSDate by passing in a string that cannot be parsed correctly  This is because of the forced unwrap of the optional value returned by dateFromString  If you wanted to return a nil on bad parses  you would ideally use a failible initializer  but you cannot do that now  June 2015   because of a limitation in Swift 1 2  so then you re next best choice is to use a class factory method   A more elaborate example  which addresses both issues  is here  https   gist github com algal 09b08515460b7bd229fa      Update for Swift 5  extension Date       init   dateString String            let dateStringFormatter   DateFormatter           dateStringFormatter dateFormat    yyyy-MM-dd          dateStringFormatter locale   NSLocale localeIdentifier   en US POSIX   as Locale         let date   dateStringFormatter date from  dateString           self init timeInterval 0  since date

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Swift doesn t have its own Date type  but you to use the existing Cocoa NSDate type  e g   class Date        class func from year  Int  month  Int  day  Int  - gt  Date           let gregorianCalendar   NSCalendar calendarIdentifier   gregorian            var dateComponents   DateComponents           dateComponents year   year         dateComponents month   month         dateComponents day   day          let date   gregorianCalendar date from  dateComponents           return date            class func parse   string  String  format  String    yyyy-MM-dd   - gt  Date           let dateFormatter   DateFormatter           dateFormatter timeZone   NSTimeZone default         dateFormatter dateFormat   format          let date   dateFormatter date from  string           return date           Which you can use like   var date   Date parse  2014-05-20   var date   Date from year  2014  month  05  day  20

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According to Apple documentation  Example    var myObject   NSDate   let futureDate   myObject dateByAddingTimeInterval 10  let timeSinceNow   myObject timeIntervalSinceNow

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According to  mythz answer  I decide to post updated version of his extension using swift3 syntax   extension Date       static func from   year  Int    month  Int    day  Int  - gt  Date                let gregorianCalendar   Calendar identifier   gregorian          let dateComponents   DateComponents calendar  gregorianCalendar  year  year  month  month  day  day          return gregorianCalendar date from  dateComponents            I don t use parse method  but if someone needs  I will update this post

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I often have a need to combine date values from one place with time values for another   I wrote a helper function to accomplish this   let startDateTimeComponents   NSDateComponents   startDateTimeComponents year   NSCalendar currentCalendar   components NSCalendarUnit Year  fromDate  date  year startDateTimeComponents month   NSCalendar currentCalendar   components NSCalendarUnit Month  fromDate  date  month startDateTimeComponents day   NSCalendar currentCalendar   components NSCalendarUnit Day  fromDate  date  day startDateTimeComponents hour   NSCalendar currentCalendar   components NSCalendarUnit Hour  fromDate  time  hour startDateTimeComponents minute   NSCalendar currentCalendar   components NSCalendarUnit Minute  fromDate  time  minute let startDateCalendar   NSCalendar identifier  NSCalendarIdentifierGregorian  combinedDateTime   startDateCalendar  dateFromComponents startDateTimeComponents

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According to Apple s Data Formatting Guide     Creating a date formatter is not a cheap operation  If you are likely   to use a formatter frequently  it is typically more efficient to cache   a single instance than to create and dispose of multiple instances    One approach is to use a static variable   And while I agree with  Leon that this should be failable initializer  when you enter seed data  we could have one that isn t failable  just like there is UIImage imageLiteralResourceName      So here s my approach   extension DateFormatter     static let yyyyMMdd  DateFormatter         let formatter   DateFormatter       formatter dateFormat    yyyy-MM-dd      formatter calendar   Calendar identifier   iso8601      formatter timeZone   TimeZone secondsFromGMT  0      formatter locale   Locale identifier   en US POSIX       return formatter          extension Date       init  yyyyMMdd  String            guard let date   DateFormatter yyyyMMdd date from  yyyyMMdd  else   return nil           self init timeInterval  0  since  date             init dateLiteralString yyyyMMdd  String            let date   DateFormatter yyyyMMdd date from  yyyyMMdd           self init timeInterval  0  since  date            And now enjoy simply calling      For seed data Date dateLiteralString   2020-03-30       When parsing data guard let date   Date yyyyMMdd   2020-03-30   else   return nil

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In  Swift 3 0 you have  set date object  for this way   extension Date       init dateString String            let dateStringFormatter   DateFormatter           dateStringFormatter dateFormat    yyyy-MM-dd          dateStringFormatter locale   Locale identifier   en US POSIX           let d   dateStringFormatter date from  dateString           self timeInterval 0  since d

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