ISO8601DateFormatter doesn't parse ISO date string

Question

I'm trying to parse this

2017-01-23T10:12:31.484Z

using native ISO8601DateFormatter class provided by iOS 10 but always fails. If the string not contains milliseconds, the Date object is created without problems.

I'm tried this and many options combination but always fails...

let formatter = ISO8601DateFormatter()
formatter.timeZone = TimeZone(secondsFromGMT: 0)
formatter.formatOptions = [.withInternetDateTime, .withDashSeparatorInDate, .withColonSeparatorInTime, .withColonSeparatorInTimeZone, .withFullTime]

Any idea? Thanks!

Answer 1

Prior to macOS 10.13 / iOS 11 ISO8601DateFormatter does not support date strings including milliseconds.

A workaround is to remove the millisecond part with regular expression.

let isoDateString = "2017-01-23T10:12:31.484Z"
let trimmedIsoString = isoDateString.replacingOccurrences(of: "\\.\\d+", with: "", options: .regularExpression)
let formatter = ISO8601DateFormatter()
let date = formatter.date(from: trimmedIsoString)

In macOS 10.13+ / iOS 11+ a new option is added to support fractional seconds:

static var withFractionalSeconds: ISO8601DateFormatter.Options { get }

let isoDateString = "2017-01-23T10:12:31.484Z"
let formatter = ISO8601DateFormatter()
formatter.formatOptions =  [.withInternetDateTime, .withFractionalSeconds]
let date = formatter.date(from: isoDateString)

Answer 2

For people that are not ready to go to iOS 11 yet, you can always create your own formatter to handle milliseconds, e.g.:

extension DateFormatter {
    static var iSO8601DateWithMillisec: DateFormatter {
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"
        return dateFormatter
    }
}

Usage:

let formater = DateFormatter.iSO8601DateWithMillisec
let date = formater.date(from: "2017-01-23T10:12:31.484Z")!
print(date) // output: 2017-01-23 10:12:31 +0000

It is slightly more elegant than writing a regex to strip out the milliseconds from the input string.

Answer 3

Maybe this will help to decode slightly different formats:

extension JSONDecoder {
    enum DateDecodeError: String, Error {
        case invalidDate
    }

    static var bestDateAttemptDecoder: JSONDecoder {
        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .custom({ (decoder) -> Date in
            let container = try decoder.singleValueContainer()
            if let dateSecs = try? container.decode(Double.self) {
                return Date(timeIntervalSince1970: dateSecs)
            }

            if let dateSecs = try? container.decode(UInt.self) {
                return Date(timeIntervalSince1970: TimeInterval(dateSecs))
            }

            let dateStr = try container.decode(String.self)
            let isoFormatter = ISO8601DateFormatter()
            isoFormatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
            if let date = isoFormatter.date(from: dateStr) {
                return date
            }

            isoFormatter.formatOptions = [.withInternetDateTime ]
            if let date = isoFormatter.date(from: dateStr) {
                return date
            }

            log.warning("Cannot decode date");
            throw DateDecodeError.invalidDate
        })

        return decoder
    }
}

From: https://gist.github.com/th3m477/442a0d1da6354dd3b84e3b71df5dca6a

Answer 4

I encountered same issue some months ago. And here's my solution for reference:

// *****************************************
// MARK: - Formatter extension
// *****************************************
extension Formatter {
    static let iso8601: ISO8601DateFormatter = {
        let formatter = ISO8601DateFormatter()
        formatter.timeZone = TimeZone.current 
        formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
        return formatter
    }()
    static let iso8601NoSecond: ISO8601DateFormatter = {
        let formatter = ISO8601DateFormatter()
        formatter.timeZone = TimeZone.current 
        formatter.formatOptions = [.withInternetDateTime]
        return formatter
    }()
}

// *****************************************
// MARK: - ISO8601 helper
// *****************************************
    func getDateFrom(DateString8601 dateString:String) -> Date?
    {
        if let date = Formatter.iso8601.date(from: dateString)  {
            return date
        }
        if let date = Formatter.iso8601NoSecond.date(from: dateString)  {
            return date
        }
        return nil
    }

// *****************************************
// usage
// *****************************************
    let d = getDateFrom(DateString8601: "2017-01-23T10:12:31.484Z")
    print("2017-01-23T10:12:31.484Z millis= ", d?.timeIntervalSinceReferenceDate)

    let d2 = getDateFrom(DateString8601: "2017-01-23T10:12:31Z")
    print("2017-01-23T10:12:31Z millis= ", d2?.timeIntervalSinceReferenceDate)


// *****************************************
// result
// *****************************************
2017-01-23T10:12:31.484Z millis=  Optional(506859151.48399997)
2017-01-23T10:12:31Z millis=  Optional(506859151.0)