We use Disqus for our comments functionality. Its comments timestamp is in ISO8601 date format, e.g. "2019-12-11T01:45:23". We tried to parse that string with DateFormatter, set up like this:
let dateFormatter = DateFormatter()
dateFormatter.timeZone = TimeZone(secondsFromGMT: 0)
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
return dateFormatter
It works well for most users. However, we receive reports for a small amount of users that the formatter returns nil. Our initial hypothesis for the cause are as follows.
the date format "yyyy-MM-dd'T'HH:mm:ss" was wrong
locale
timezone
daylight saving makes some time theoretically non-existent
calendar
or something else...
All of them are parameters we use to set up the DateFormatter. We tried many combinations, including ones we got from user reports. We tried the same date, locale, timezone, calendar, and the time itself as in user reports.
locale: en_GB, timezone: Europe/London, calendar: gregorian, isDaylightSavingTime: 1
locale: en_TR, timezone: Etc/GMT-3, calendar: gregorian, isDaylightSavingTime: 0
locale: es_MX, timezone: America/Mexico_City, calendar: gregorian, isDaylightSavingTime: 1
locale: en_ID, timezone: Asia/Jakarta, calendar: gregorian, isDaylightSavingTime: 0
But we could not reproduce.
Moreover, we did another test with a bunch of dates spreading throughout the year. And perform hidden parsing test on every user. It seems on device that returns nil date, it returns nil for EVERY date. The date string list looks like this...
[
"2019-01-11T01:45:23",
"2019-02-11T01:45:23",
"2019-03-11T01:45:23",
"2019-04-10T01:45:23",
"2019-04-11T01:45:23",
"2019-04-12T01:45:23",
"2019-05-11T01:45:23",
"2019-06-11T01:45:23",
"2019-07-11T01:45:23",
"2019-08-11T01:45:23",
"2019-09-11T01:45:23",
"2019-10-11T01:45:23",
"2019-11-11T01:45:23",
"2019-12-11T01:45:23",
])
We later found that there is another date formatter called ISO8601DateFormatter. It seems to be more appropriate for this parsing. Here is the how we set it up.
let dateFormatter = ISO8601DateFormatter()
dateFormatter.timeZone = TimeZone(secondsFromGMT: 0)
dateFormatter.formatOptions = [.withFullDate, .withTime, .withDashSeparatorInDate, .withColonSeparatorInTime]
return dateFormatter
With this ISO8601DateFormatter, the issue is fixed.
But I still want to know what can cause DateFormatter to fail on some device? Is there other factors than locale/isDaylightSavingTime/timezone that I'm not aware of?
Is it the user's setting for 12-hour vs. 24-hour clock?
iOS can change a date formatter's format string to match the user's settings. The locale en_US_POSIX is recommended for fixed formats to prevent format changes due to user settings.
Please use ISO8601 date format with timezone
"2019-12-11T01:45:23.000Z"
Format:
"XXXX-XX-XX" = year, month, day,
"T" = separator
"XX:XX:XX.XXX" = hour, minute, seconds, milliseconds
"Z" = timezone designator for zero offset, a.k.a. UTC, GMT, Zulu time
let dateFormatter = DateFormatter()
dateFormatter.timeZone = TimeZone(secondsFromGMT: 0)
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
return dateFormatter
For anybody still facing this issue, what worked for me was to set dateFormatter.isLenient = true as it is described here: DateFormatter returning nil for a valid Date string
Related
In our app there is the issue with creating a date from string but is only reproducible with a very specific combination. Unfortunately, there is no way of getting it from the user that experienced the issue, so I decided to just go for it and try every possible combination:
import Foundation
var dateOnlyDateFormatter: (String, String) -> DateFormatter = { timeZoneS, localeS in
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd"
formatter.timeZone = TimeZone(identifier: timeZoneS)
formatter.locale = Locale(identifier: localeS)
return formatter
}
let date = "2022-05-27"
let time = "06:15"
for timeZone in TimeZone.knownTimeZoneIdentifiers {
for locale in Locale.availableIdentifiers {
let dateFormatter = dateOnlyDateFormatter(timeZone, locale)
let printDate = dateFormatter.date(from: date)
if printDate == nil {
print("TimeZone: \(timeZone), Locale: \(locale)")
}
}
}
The result:
TimeZone: America/Asuncion, Locale: ar_SA
TimeZone: America/Asuncion, Locale: en_SA
I am not too sure what is the best way to handle this issue. Obviously our BE could return date using one specific Locale, like en_US_POSIX, but I have very little control over that, being a part of a much bigger older system. Has anybody experienced an issue like that?
If you read the "Working With Fixed Format Date Representations" section of the DateFormatter docs, you'll find:
For most fixed formats, you should also set the locale property to a POSIX locale ("en_US_POSIX"), and set the timeZone property to UTC.
You should probably just follow the advice here... But here's possibly why SA and the Paraguay timezone produces nil.
Further down that section, there is a link to a technical Q&A where this is explained in more detail. The part that is most related to your problem is:
A user can change their calendar (using System Preferences > Language & Region > Calendar on OS X, or Settings > General > International > Calendar on iOS). In that case NSDateFormatter will treat the numbers in the string you parse as if they were in the user's chosen calendar. For example, if the user selects the Buddhist calendar, parsing the year "2010" will yield an NSDate in 1467, because the year 2010 on the Buddhist calendar was the year 1467 on the (Gregorian) calendar that we use day-to-day.
In the locale SA, the numbers of your date string seem to be interpreted using the Islamic Calendar. Take a look at today's date when formatted with en_SA and America/New_York.
let dateFormatter = dateOnlyDateFormatter("America/New_York", "en_SA")
let printDate = dateFormatter.string(from: .init())
print(printDate)
// 1443-10-26
Also take a look at the non-nil dates that is parsed by en_SA and America/New_York
let dateFormatter = dateOnlyDateFormatter("America/New_York", "en_SA")
let printDate = dateFormatter.date(from: date)
print(printDate)
// 2583-10-05 04:00:00 +0000
Notice that 10-05 is the first Sunday of the year 2583 (See this calendar). If Paraguay still uses the same DST rules as it does now in 2583, then it would mean that there is a DST gap transition at 2583-10-05 00:00:00, starting the DST period. The hour starting from 00:00:00 would be skipped, so 00:00:00 would not exist.
When parsing a date only, DateFormatter would try to set the time components to be 00:00:00 in the timezone of the formatter, but 00:00:00 does not exist, so the parsing fails.
In any case, just set locale to posix and timeZone to UTC when you have set dateFormat.
So if you use 'time' like this, there will be no nil values:
let dateOnlyDateFormatter: (String, String) -> DateFormatter = { timeZoneS, localeS in
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd HH:mm"
formatter.timeZone = TimeZone(identifier: timeZoneS)
formatter.locale = Locale(identifier: localeS)
return formatter
}
let date = "2022-05-27 06:15"
//let time = "06:15"
for timeZone in TimeZone.knownTimeZoneIdentifiers {
for locale in Locale.availableIdentifiers {
let dateFormatter = dateOnlyDateFormatter(timeZone, locale)
let printDate = dateFormatter.date(from: date)
if printDate == nil {
print(">>>>>>>> TimeZone: \(timeZone), Locale: \(locale)")
} else {
print("..... \(printDate)")
}
}
}
I am struggling with Date and I'm assuming is TimeZone.
Currently I get from my backend a string like this "2020-04-07" and when I try to convert it to date it turns into 2020-04-06 22:00:00 +0000. I am in Spain (UTC+2) which I guess this is why it removes 2 hours?
This is my date formatter:
var dateFormatter: DateFormatter = {
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
dateFormatter.timeZone = TimeZone.current
return dateFormatter
}()
And I call it dateFormatter.date(from: startDateString)
I am setting my current timezone but seems to be ignoring it or am I missing something?
I have followed a lot of answers from here but it's always the same result.
Thank you
The Date object does not have any inherent locale / time zone. It just represents a moment in time. If you want to see that Date as a string in a specific locale/time zone you have to use a date formatter. Or there's descriptionWithLocale. If you use print it will print a debug description of the Date instance in UTC.
I have the following string:
let dateString = "2018-04-18T04:54:00-04:00"
I initialize a Date via the ISO8601DateForamtter by doing the following:
let formatter = ISO8601DateFormatter()
let date = formatter.date(from: dateString)
If I print the date, I get the following:
Apr 18, 2018 at 1:54am
The formatter is automatically converting the time into my local time. How can I prevent accounting for my time zone? For example, I want the Date object to show the following instead:
Apr 18, 2018 at 4:54am
With ISO8601, 2018-04-18T04:54:00-04:00 means 2018-04-18 04:54:00 in GMT -4h. To print the time as it is in the original string, you need to create a date formatter with the specific time zone which is -4.
let dateFormatter = DateFormatter()
dateFormatter.timeZone = TimeZone(secondsFromGMT: -4 * 60 * 60)
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
print(dateFormatter.string(from: date))
You will get
2018-04-17 04:54:00
FYI, I'm adding a link for ISO8601
You need to parse the timezone from your date string and use it to set the timezone from your date formatter:
func secondsFromGMT(from string: String) -> Int {
guard !string.hasSuffix("Z") else { return 0 }
let timeZone = string.suffix(6)
let comps = timeZone.components(separatedBy: ":")
guard let hours = comps.first,
let minutes = comps.last,
let hr = Int(hours),
let min = Int(minutes) else { return 0 }
return hr * 3600 + min * 60
}
let dateString = "2018-04-18T04:54:00-04:00"
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssxxxxx"
formatter.locale = Locale(identifier: "en_US_POSIX")
if let dateFromString = formatter.date(from: dateString) {
formatter.timeZone = TimeZone(secondsFromGMT: secondsFromGMT(from: dateString))
formatter.dateFormat = "MMM dd, yyyy 'at' h:mma"
formatter.amSymbol = "am"
formatter.pmSymbol = "pm"
print(formatter.string(from: dateFromString)) // Apr 18, 2018 at 4:54am
}
Instead of logging the Date directly, have a look at the string(from:timeZone:formatOptions:) method on ISO8601DateFormatter. With this, you should be able to get a date string for any time zone you desire.
You should set your formatter to the appropriate timezone such as (UTC example below):
formatter.timeZone = TimeZone(identifier: "UTC")
or alternatively specify against GMT:
formatter.timeZone = TimeZone(secondsFromGMT: 0)
The date that you are receiving from your current formatter is technically correct. Setting the date backwards as described in the currently accepted answer is not advised because you are effectively hard-coding an intended time zone. As soon as your device enters another time zone (or if a user downloads your app outside of the current time zone), your information will be incorrect.
If you are trying to display this time in the UTC time zone, you need to use another formatter to correctly format the output in the target time zone.
let utcFormatter = DateFormatter()
utcFormatter.timeZone = TimeZone(secondsFromGMT: 0)
// Perform any other transformations you'd like
let output = utcFormatter.string(from: date)
But why is your original date correct?
The Date API is incredibly robust and doing a lot of things under-the-hood, but is effectively implemented using a simple Double. The automaic time-zone information that it's displaying to you is an abstraction to make it easier to reason about. A date technically has no knowledge of what time zone it's in – but converting it to a string implicitly applies an inferred date formatter on the date and returns information it thinks will be most useful to you.
If you're doing manipulations on a date, you're likely using the Calendar API. You typically get a new instance from using Calendar.current, which will create a new calendar with your current time zone information. You can change the represented time zone of the calendar like this:
var calendar = Calendar.current
calendar.timeZone = TimeZone(secondsFromGMT: 0)
This will give you relative dates that will work in any time zone without modifying the base Date object that you're working with.
I am new to iOS development, being an Android developer I am used to use have an object that saves a datetime with a given timezone (from Joda-Time library).
After reading the iOS documentation about dates and times (https://developer.apple.com/documentation/foundation/dates_and_times) I still have doubts about which class should I use to save datetimes. Given the Date/NSDate class description "A specific point in time, independent of any calendar or time zone." it seems very useless because it is timezone independent and time without a timezone does not make any sense, since it does not have any context.
My real problem (TL;DR):
I have a database where date times are stored in UTC like this "yyyy-MM-dd hh:mm:ss". I would like to init an object with some kind of DateFormatter (string with this format "yyyy-MM-dd hh:mm:ss") plus a timezone (UTC) to easily convert to any Timezone that I want (to show to the user on his default timezone time). How can I accomplish this in iOS?
Edit: Imagine I have a class Event with a title and a start time. Title is a String, what start time should be?
You use a DateFormatter for this.
let formatter = DateFormatter()
formatter.calendar = Calendar(identifier: .iso8601)
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
formatter.timeZone = TimeZone(secondsFromGMT: 0)
The formatter.locale sets the current locale for the user and formatter.dateFormat sets the desired date format. In your case yyyy-MM-dd HH:mm:ss.
To call it simply:
let utcDateFromServer = "2017-01-01 22:10:10"
let date = formatter.date(from: utcDateFromServer)
A Date is a point in time, as mentioned in other comments & in the documentation.
If you want to convert the UTC time into local time, you'll need to first convert the String "yyyy-MM-dd hh:mm:ss" from your database into a Date using DateFormatter.
let dateStringUTC = "2018-01-01 00:00:00"
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd hh:mm:ss"
//Set the input timezone (if you don't set anything, the default is user's local time)
dateFormatter.timeZone = TimeZone(abbreviation: "UTC")
let date : Date = dateFormatter.date(from: dateStringUTC)!
Then convert the Date back into String using DateFormatter with the respective TimeZone
let outputDateFormatter = DateFormatter()
outputDateFormatter.dateFormat = "yyyy-MM-dd hh:mm:ss"
//Set the output timezone (if you don't set anything, the default is user's local time)
//outputDateFormatter.timeZone = someTimeZone
let dateString = outputDateFormatter.string(from: date)
print(dateString)
Output: 2017-12-31 17:00:00
And you can just change the input and output timezone to do the opposite.
I have a string getting from server as "yyyy-MM-dd'T'HH:mm:ss.SSS'Z"
I convert this string into NSDate by this formate.
class func convertUTCDateToLocateDate(dateStr:String) -> NSDate{
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
dateFormatter.timeZone = NSTimeZone(name: "UTC")
let date = dateFormatter.dateFromString(dateStr)
dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z"
dateFormatter.timeZone = NSTimeZone.localTimeZone()
let timeStamp = dateFormatter.stringFromDate(date!)
let dateForm = NSDateFormatter()
dateForm.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
dateForm.timeZone = NSTimeZone.localTimeZone()
let dateObj = dateForm.dateFromString(timeStamp)
return dateObj!
}
Suppose the parameter string is "2016-11-05T12:00:00.000Z" but when i convert this string and return a NSDate object it doesn't change the time according to my local time. I get my correct time in the timeStamp string (in above code). But when i try to convert that timeStamp string into NSDate it again shows that date and time which i got as a parameter.
You shouldnt change a NSDate's time. NSDates are just a point in time, counted by seconds. They have no clue about timezones, days, month, years, hours, minutes, seconds,… If printed directly they will always output the time in UTC.
If you change the date to show you the time of your timezone you are actually altering the time in UTC — hence your date becomes representing another point in time, no matter of the timezone.
Keep them intact by not altering them, instead when you need to display them do it via a date formatter.
If you need to do time calculations that are independent of timezones you also can work with NSDateComponents instead.
NSDate doesn't have a timezone. It's a point in time, independent of anything, especially timezones. You cannot "convert a UTC NSDate to a local NSDate", the statement itself doesn't make any sense.