Incorrect timezone in Swift's DateInterval

Question

I want to store some data as a dictionary in my app relative to the date this data was created. It should look something like this:

// hours
[ 17:00 - 18:00 : 34.5,
  18:00 - 19:00 : 41.2,
... ]

// days
[ 2017-11-19 - 2017-11-20 : 37.9,
  2017-11-20 - 2017-11-21 : 31.1,
... ]

A DateInterval structure seems to be a perfect candidate for a key in this dictionary. But as I ran some basic tests I found that while date created with Date() init represents correct information on a given moment in time, the DateInterval structure from Calendar.current appears to be defaulting to GMT+0 as a timezone, so I'm getting following output:

let date = Date() //outputs "Nov 20, 2017 at 10:32 PM"
let hourInterval = Calendar.current.dateInterval(of: .hour, for: date)
//outputs: 2017-11-20 20:00:00 +0000 to 2017-11-20 21:00:00 +0000

So it's 2 hours off my/user's timezone. What is the correct way to use DateInterval so it doesn't shift in timezones?

did you check [converting date between timezones](https://stackoverflow.com/questions/38641982/converting-date-between-timezones-swift) — zombie, Nov 20 '17 at 21:11

score 1 · Accepted Answer · answered Nov 20 '17 at 21:18

The internal structure of dates in iOS is always GMT. What you're seeing is the string representation. The internal dates are still consistent with one another. Consider this playground code:

//: Playground - noun: a place where people can play

import UIKit
import XCTest
import PlaygroundSupport


let fourHours:Double = -1 * 60 * 60 * 4
var newDate = Date()
let oldDate = Date(timeInterval: fourHours, since: newDate)
let interval = DateInterval(start: oldDate, end: newDate)

let hourInterval = Calendar.current.dateInterval(of: .hour, for: newDate)

The output looks like this:

Even though the dates are show as local time (EST) the printable representation is in GMT. The times are offset though, so 'Nov 20, 2017 at 4:14 PM EST' is equivalent to '2017-11-20 21:14:09 +0000'. You can always retrieve the original date objects from the DateInterval with

hourInterval?.start
hourInterval?.end

Thanks for clearing the concept)) Just got confused because string representations will be used to display information in charts and I was afraid all components would get messed up. — Denys Triasunov, Nov 20 '17 at 22:07

Incorrect timezone in Swift's DateInterval

1 Answers1