Get UTC date/time string for current time using NSCalendar

utcDateTime.m

        NSDate *date = [NSDate date];

        NSCalendar *utcCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
        utcCalendar.timeZone = [NSTimeZone timeZoneWithAbbreviation:@"UTC"];

        unsigned ymdhmsUnitFlags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay| NSCalendarUnitHour | NSCalendarUnitMinute |  NSCalendarUnitSecond;

        NSDateComponents *utcDateComponents = [utcCalendar components:ymdhmsUnitFlags fromDate:date];

        // Create string of form "yyyy-mm-dd hh:mm:ss"
        NSString *utcDateTime = [NSString stringWithFormat:@"%04lu-%02lu-%02lu %02lu:%02lu:%02lu",
                                 (unsigned long)[utcDateComponents year],
                                 (unsigned long)[utcDateComponents month],
                                 (unsigned long)[utcDateComponents day],
                                 (unsigned long)[utcDateComponents hour],
                                 (unsigned long)[utcDateComponents minute],
                                 (unsigned long)[utcDateComponents second]];

utcDateTime.swift

import Foundation

let date = NSDate()

if let utcCalendar = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian) {
    if let utcTimeZone = NSTimeZone(abbreviation: "UTC") {

        utcCalendar.timeZone = utcTimeZone

        let ymdhmsUnitFlags: NSCalendarUnit = .YearCalendarUnit | .MonthCalendarUnit | .DayCalendarUnit | .HourCalendarUnit | .MinuteCalendarUnit | .SecondCalendarUnit

        let utcDateComponents = utcCalendar.components(ymdhmsUnitFlags, fromDate: date)

        // Create string of form "yyyy-mm-dd hh:mm:ss"
        let utcDateTimeString = NSString(format: "%04u-%02u-%02u %02u:%02u:%02u",
            UInt(utcDateComponents.year),
            UInt(utcDateComponents.month),
            UInt(utcDateComponents.day),
            UInt(utcDateComponents.hour),
            UInt(utcDateComponents.minute),
            UInt(utcDateComponents.second))
    }
}

Thank you for this time saver!

No '|' candidates produce the expected contextual result type 'NSCalendarUnit' in swift 2.1

let ymdhmsUnitFlags: NSCalendarUnit = [NSCalendarUnit.Year , .Month ,.Day,.Hour , .Minute , .Second]