Convert date between time zones

Question

I have a date stored in my online server database, which is located at GMT. I download the date and convert it to the user's time zone using the following code:

 if let messagedate = oneitem["timestamp"] as? String {
     let dateFormatter = NSDateFormatter()
     dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
     let date = dateFormatter.dateFromString(messagedate)
     let source_timezone = NSTimeZone(abbreviation: "GMT")
     let local_timezone = NSTimeZone.systemTimeZone()
     let source_EDT_offset = source_timezone?.secondsFromGMTForDate(date!)
     let destination_EDT_offset = local_timezone.secondsFromGMTForDate(date!)
     let time_interval : NSTimeInterval = Double(destination_EDT_offset - source_EDT_offset!)


     let final_date = NSDate(timeInterval: time_interval, sinceDate: date!)
     curr_item.date = final_date
 }

Now I need to convert the date back to in GMTorder to inform the server about it, however I am not sure how to convert it back to GMT.

Answer 1

Could you use your data format again with another time zone and convert it? For instance,

dateFormatter.timeZone = NSTimeZone(abbreviation: "GMT")
let gmtDate = dateFormatter.dateFromString(string: "your old date as string here")

Answer 2

about 50 times more effective

extension Date {
    func convertToLocalTime(fromTimeZone timeZoneAbbreviation: String) -> Date? {
        if let timeZone = TimeZone(abbreviation: timeZoneAbbreviation) {
            let targetOffset = TimeInterval(timeZone.secondsFromGMT(for: self))
            let localOffeset = TimeInterval(TimeZone.autoupdatingCurrent.secondsFromGMT(for: self))

            return self.addingTimeInterval(targetOffset - localOffeset)
        }

        return nil
    }
}

Answer 3

NSDate GMT/UTC, . UTC , ( NSDateFormatter) , .

Answer 4

• GMT dateFormatter, NSDate UTC ( NSDates UTC - ).
• , NSDateFormatter ( )
• , dateFormatter