How to extract TimeZone from Date object? - swift

Question

I have an ISO-8601 date string like this: "2017-02-07T00:00:00-08:00".
How can I extract the TimeZone object from this date?

Answer 1

Unfortunately, DateFormatter is no help since you don't want a Date nor does it provide any information about any timezone info about a parsed date string. And TimeZone doesn't have any initializer that can parse a timezone offset string.
So you will have to do the work yourself. Since you have a fixed format date string, you know the timezone offset is always going to be the last 6 characters of the string. The last 2 of those are the number of minutes and the first 3 of those are the number of hours (including the sign).
Extract these two substrings (hours and minutes) from the date string. Convert them both to Int. Then do some simple math to calculate an offset in seconds (hours * 3600 + minutes * 60).
Once you have that offset in seconds, you can create a TimeZone instance using the init(secondsFromGMT:) initializer.

Answer 2

Using rmaddys proposed solution, I wrote an extension for TimeZone which should do the job.
extension TimeZone {
init?(iso8601String: String) {
let timeZoneString = String(iso8601String.suffix(6))
let sign = String(timeZoneString.prefix(1))
guard sign == "+" || sign == "-" else {
return nil
}
let fullTimeString = timeZoneString.filter("0123456789".contains)
guard fullTimeString.count == 4 else {
return nil
}
guard let hours = Int(sign+fullTimeString.prefix(2)), let minutes = Int(sign+fullTimeString.suffix(2)) else {
return nil
}
let secondsFromGMT = hours * 3600 + minutes * 60
self.init(secondsFromGMT: secondsFromGMT)
}
}

Answer 3

You could create a date formatter that only returns the time zone such as below. Change the abbreviation to whichever time zone you are looking for.
let timeZoneOnlyDateFormatter: DateFormatter = {
let formatter = DateFormatter()
formatter.timeZone = TimeZone(abbreviation: "UTC")
formatter.dateStyle = .none
formatter.timeStyle = .none
return formatter
}()
And use these functions to convert it to a string or convert your string to a date.
func formatDateIntoString(date: Date, dateFormatter: DateFormatter) -> String {
return dateFormatter.string(from: date)
}
func formatStringIntoDate(string: String, dateFormatter: DateFormatter) -> Date! {
return dateFormatter.date(from: string)
}