I found that DateFormatter date(from:) method can't parse a couple of specific dates. Method returns nil for the 1st april of 1981-1984 years. Is it a bug of Foundation? What can we do to perform parsing of such dates?
Xcode 8.0, iOS SDK 10.0. Here is a screenshot of a short playground example:
This problem occurs if daylight saving time starts exactly on
midnight, as it was the case in Moscow in the years 1981–1984 (see for example Clock Changes in Moscow, Russia (Moskva)).
This was also observed in
Why does NSDateFormatter return nil date for these 4 time zones? and
Why NSDateFormatter is returning null for a 19/10/2014 in a Brazilian time zone?
For example, at midnight of April 1st 1984, the clocks were adjusted one hour forward, which means that the date "1984-04-01 00:00"
does not exist in that timezone:
let dFmt = DateFormatter()
dFmt.dateFormat = "yyyy-MM-dd"
dFmt.timeZone = TimeZone(identifier: "Europe/Moscow")
print(dFmt.date(from: "1984-04-01")) // nil
As a solution, you can tell the date formatter to be "lenient":
dFmt.isLenient = true
and then it will return the first valid date on that day:
dFmt.isLenient = true
if let date = dFmt.date(from: "1984-04-01") {
dFmt.dateFormat = "yyyy-MM-dd HH:mm:ss"
print(dFmt.string(from: date))
}
// 1984-04-01 01:00:00
A different solution
was given by rob mayoff, which is to make the date formatter use noon instead of midnight as the
default date. Here is a translation of rob's code from Objective-C to Swift:
let noon = DateComponents(calendar: dFmt.calendar, timeZone: dFmt.timeZone,
year: 2001, month: 1, day: 1, hour: 12, minute: 0, second: 0)
dFmt.defaultDate = noon.date
if let date = dFmt.date(from: "1984-04-01") {
dFmt.dateFormat = "yyyy-MM-dd HH:mm:ss"
print(dFmt.string(from: date))
}
// 1984-04-01 12:00:00
Related
I wrote a date reformatter but it appears Swift's date formatter itself is ignoring the months. The documentation says this shouldn't be happening. How do I make it not ignore months?
let testDate:String = "2020-11-22-11:00"
print("start date: ",testDate," reformatted date: ", reformatDate(dateString: testDate))
func reformatDate(dateString: String) -> String? {
print("dateString: ",dateString)
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-DD-HH:mm"
dateFormatter.timeZone = TimeZone(abbreviation: "UTC")
return dateFormatter.string(from: dateString)
}
this prints:
start date: 2020-11-22-11:00 converted date: 22-01-2020 11:00 AM
It unreasonably turns all months to 1!
Your format string is incorrect. It should be:
yyyy-MM-dd-HH:mm
and
dd-MM-yyyy h:mm a
dd means day-of-month, whereas DD means day-of-year.
Note that you should also do:
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
whenever you are using a custom date format.
Parsing 2020-11-22-11:00 with yyyy-MM-DD-HH:mm means that you want the twenty second day of the year 2020, in the month November. That makes no sense, and DateFormatter ends up ignoring the month because apparently day-of-year is a "stronger" date component. The 22nd day of any year is the 22nd of January.
Then, when you format the parsed date with DD-MM-yyyy h:mm a, the month component gets displayed as 01, and the day-of-year is still displayed as 22.
Here are some useful links to learn about format specifiers, you'll just how much lowercase/uppercase matters.
NSDateFormatter.com
TR-35
I'm using FSCalendar in a Swift app, and when user selects a day, I'm printing the selected day, and the it prints the previous day, at 23:00. I'm not sure why and how can I solve this. I'm in spain. Maybe it's related with where you are and your local hour?
This is how I'm printing the selected day:
extension CalendarDataViewViewController: FSCalendarDataSource {
func calendar(_ calendar: FSCalendar, didSelect date: Date, at monthPosition: FSCalendarMonthPosition) {
let df = DateFormatter()
df.dateFormat = "yyyy-MM-dd hh:mm:ss"
let now = df.string(from: date)
logger.debug("Date: \(date)")
}
}
And this is what it's printed when I select 18 march:
21:01:24.646 💚 DEBUG CalendarDataViewViewController.calendar():258 - Date: 2021-03-17 23:00:00 +0000
Your code creates a date formatter, converts the returned date to a date string with that formatter, and then ignores that and simply prints the date, which is being displayed in UTC. (Note the output Date: 2021-03-17 23:00:00 +0000)
Change your log command to read:
logger.debug("Date: \(now)")
And by the way, the variable name now is a terrible choice for holding a user-selected date that is not the current date.
I'd suggest renaming the returned date parameter selectedDate and the String output of the formatter as selectedDateString
Edit:
Consider this code:
import Foundation
func dateStringFromDate(_ inputDate: Date) -> String {
let df = DateFormatter()
df.dateFormat = "yyyy-MM-dd hh:mm:ss a"
let dateString = df.string(from: inputDate)
return dateString
}
func isoDateStringFromDate(_ inputDate: Date) -> String {
let df = ISO8601DateFormatter()
df.formatOptions = .withInternetDateTime
df.timeZone = TimeZone.current //Force the formatter to express the time in the current time zone, including offset
let dateString = df.string(from: inputDate)
return dateString
}
let now = Date()
print("Current timezone = \(TimeZone.current)")
print("now in 'raw' format = \(now)")
let localizedDateString = DateFormatter.localizedString(from: now,
dateStyle: .medium,
timeStyle: .medium)
print("localizedString for the current date = \(localizedDateString)")
print("dateStringFromDate = \(dateStringFromDate(now))")
print("isoDateStringFromDate = \(isoDateStringFromDate(now))")
Right now, at about 9:16 PM EDT on Thursday March 18th, that logs the following:
Current timezone = America/New_York (current)
now in 'raw' format = 2021-03-19 01:16:52 +0000
localizedString for the current date = Mar 18, 2021 at 9:16:52 PM
dateStringFromDate = 2021-03-18 09:16:52 PM
isoDateStringFromDate = 2021-03-18T21:16:52-04:00
The 'raw' date format is in GMT, with an offset value of 0. In that form, in GMT, the calendar date is already March 19th. (Because GMT is 4 hours ahead of EDT)
The class function NSDateFormatter.localizedString(from:dateStyle:timeStyle) displays a date in the current time zone and using the device's locale settings. The dateStyle and timeStyle parameters give you the option to choose whether or not, and in what format (short, medium, or long) to display the date or time.
An ISO8601DateFormatter displays the date following the conventions in the ISO8601 standard. The isoDateStringFromDate(:) function above uses the .withInternetDateTime option to express the date in the ISO8601 "internet date and time" format. I forced that date to be in the local time zone, so it displays the date with a -4 hour offset from GMT (since it is EDT, eastern daylight savings time where I live.)
The function dateStringFromDate(_:) is a slight variation on your function. It returns a date string in the current time zone, using 12 hour times and an AM/PM string.
I know how to get local date and time, but what I want to do is getting the date and time from different places. For example, I want to find out what the time and date is in New York. How can i solve this simple problem?
Here is my code for local date and time :
let date = NSDate()
let calendar = Calendar.current
let components = calendar.dateComponents([.hour, .minute, .month, .year, .day, .second, .weekOfMonth], from: date as Date)
let currentDate = calendar.date(from: components)
I searched about it here, but i didn't find what i want and I'm still looking for the date libaries. If you know any source or sample to redirect me, I really appreciate that.
There are several different concepts involved here, and we need to understand (almost) all of them to get this right...
1) a Date (NSDate as was, in Swift) is an absolute point in time - it's slightly mis-named, because it has nothing to do with an actual date like 13th November 2017, because to get to that we need to define ...
2) a Calendar, because 13th November 2017 in the western Gregorian calendar could also be 23rd Safar 1439 in the Islamic calendar, or the 24th of Heshvan 5778 in the Hebrew calendar, or some other things in the many other calendars that iOS & MacOS support;
3) in turn Calendar changes not only what values are returned in the DateComponents that we have to use to unpack a Date + Calendar into days, months, years & eras (e.g. BC/AD), or even week number, etc..., but also some calendars might not have the same components as others;
4) time-of-day (as you know) depends on TimeZone, so the same absolute time can be one of many different times "o'clock" depending on where you are. It may also (as you can see in the example below) change the date as well as the "o'clock". This of course could be automatic (where you are) or set by the programmer;
5) further, we have DateFormatter (which is a convenience that wraps up DateComponents), because 13th November 2017 could be represented as 13/11/17 or 11/13/17 depending on whether you are British or American. We may also wish to choose whether we use text or numeric months, and, if displaying times, whether we want 12 hour or 24 hour format - all of these are covered by DateFormatter, but text representation may be "13e Novembre 2017" if you are French, which introduces the notion of
6) Locale, which can be set, like TimeZone, as being default (as chosen when you set up the device) or specified by the programmer.
The code you posted won't work, because all it does is takes a Date, transforms it through a Calendar to DateComponents (all good so far), but then recreates a Date from the components - all you will get is the original Date - the same absolute point in time.
What I believe from the question and your answers to questions in the comments is that you want a function that takes an absolute time (eg "now") aka a Date and displays it in a specific TimeZone. This works:
func timeComponents(date: Date, timeZone: TimeZone) -> DateComponents {
var calendar = Calendar.current
calendar.timeZone = timeZone
return calendar.dateComponents([.hour, .minute, .month, .year, .day, .second, .weekOfMonth], from: date)
}
let absTime: Date = Date() // Now
let edinburgh = TimeZone(abbreviation: "GMT")!
let newYork = TimeZone(abbreviation: "EST")!
let ec = timeComponents(date: absTime, timeZone: edinburgh)
let nycc = timeComponents(date: absTime, timeZone: newYork)
print(ec)// year: 2017 month: 11 day: 14 hour: 0 minute: 44 second: 10 weekOfMonth: 3 isLeapMonth: false
print(nycc) // year: 2017 month: 11 day: 13 hour: 19 minute: 44 second: 10 weekOfMonth: 3 isLeapMonth: false
... which I think answers the minimum of your question, but to finesse it, we need to move from DateComponents to DateFormatter
func timeString(date: Date, timeZone: TimeZone, timeStyle: DateFormatter.Style) -> String {
let dateFormatter = DateFormatter()
dateFormatter.timeZone = timeZone
dateFormatter.dateStyle = .none
dateFormatter.timeStyle = timeStyle
return dateFormatter.string(from: date)
}
let es = timeString(date: absTime, timeZone: edinburgh, timeStyle: .full)
let nycs = timeString(date: absTime, timeZone: newYork, timeStyle: .full)
print(es) // 12:44:10 AM Greenwich Mean Time
print(nycs) // 7:44:10 PM Eastern Standard Time
You can go on, and start to use Locale, if you want to internationalise your app, but I'l leave that as an exercise!
p.s. These are not all of the concepts - see here
p.p.s. See also this answer and this answer (neither duplicates)
If you just want to format the date to a string, consider using a DateFormatter instead:
let date = Date()
let formatter = DateFormatter()
formatter.timeZone = TimeZone(identifier: "America/New_York")
formatter.dateStyle = .long
formatter.timeStyle = .long
formatter.string(from: date)
If you want to get the date components and process them, use the dateComponents(in:from:) method.
let components = Calendar.current.dateComponents(in: TimeZone(identifier: "America/New_York")!, from: date)
If you don't know the time zone of the place you are searching for, you can use the CoreLocation's CLGeocoder and search on an address string. Then you can get the timezone for that place and translate that into the time you're looking for:
let geocoder = CLGeocoder()
geocoder.geocodeAddressString("New York, New York") { (placemarks, error) in
guard error == nil else {
print("Error")
print(error!.localizedDescription)
return
}
guard let placemarks = placemarks,
let place = placemarks.first else {
print("No results")
return
}
if let timeZone = place.timeZone {
print("TimeZone: \(timeZone.identifier)")
// TimeZone: America/New_York
//Ignore the time zone offset from this one, it will be the difference between the current time and the new york time
let dateInNewYork = Date().addingTimeInterval(TimeInterval.init(timeZone.secondsFromGMT()))
print(dateInNewYork)
// 2017-11-13 15:03:05 +0000
//Or
let formatter = DateFormatter()
formatter.timeZone = TimeZone(identifier: timeZone.identifier)
formatter.dateStyle = .long
formatter.timeStyle = .long
let formattedDateInNewYork = formatter.string(from: Date())
print(formattedDateInNewYork)
// November 13, 2017 at 3:03:05 PM EST
//Or
let components = Calendar.current.dateComponents(in: TimeZone(identifier: timeZone.identifier)!, from: Date())
print(components.date!)
// 2017-11-13 20:03:05 +0000
}
}
Something strange happen to me.
I'm not able to convert this specific date (1994-04-01) String.
Can anyone check this and let me know if it reproduce in your code?
Steps to Reproduce:
Swift:-
let dateString = "1994-04-01"
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let dateFromString = dateFormatter.date(from: dateString)
Obj c:-
NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
[formatter setDateFormat:#"yyyy-MM-dd"];
NSString *birthdayStr = #"1994-04-01";
NSDate *birthday = [formatter dateFromString:birthdayStr];
Expected Results:
birthday = 1994-03-31 21:00:00 +0000
In UTC
Actual Results:
birthday = nil
Version:
Xcode ver :- Version 8.1 (8B62)
OS X ver :- 10.12.1 (16B2555)
you can try any different date then (1994-04-01) and it will work fine.
Test code:
import Foundation
for timeZoneId in TimeZone.knownTimeZoneIdentifiers {
let dateString = "1994-04-01"
let dateFormatter = DateFormatter()
dateFormatter.timeZone = TimeZone(identifier: timeZoneId)
dateFormatter.dateFormat = "yyyy-MM-dd"
if dateFormatter.date(from: dateString) == nil {
print(timeZoneId)
}
}
Output:
Asia/Amman
Asia/Damascus
Asia/Gaza
Asia/Hebron
Asia/Jerusalem
I conclude your system time zone is set to one of the ones printed. If I type “jerusalem time zone 1994” into Google, the first result tells me that Daylight Saving Time started at midnight on April 1 in 1994. This means there was no midnight. The first instant of April 1, 1994 was in fact 1 AM in that time zone.
A DateFormatter uses a time of day of midnight by default when not parsing a time of day from the string. This makes it fail when midnight doesn't exist on the date in the string.
The solution is to not use midnight as your default time of day. Noon is a much safer default time. So, one solution is to include the time of day in the input and parse it in the format:
let dateString = "1994-04-01 12:00:00"
let dateFormatter = DateFormatter()
dateFormatter.timeZone = TimeZone(identifier: timeZoneId)
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
Another solution is to give the date formatter a default date that is noon of some day:
// Reference date was 00:00:00 UTC on 1 January 2001. This is noon of the same day in UTC.
dateFormatter.defaultDate = Date(timeIntervalSinceReferenceDate: 12*60*60)
If you are going to do any date parsing or manipulation on iOS or macOS, it would be a very good idea to watch WWDC 2013 Session 227: Solutions to Common Date and Time Challenges.
i am trying to calculate the time between two dates. One of the dates is today and the other date is somewhere in the future.
The issue is the date in future is separated into two string, the first containing the date and the other containing the time for that date. When i put the two strings together to a single string and try to convert it to a NSDate i get Nil.
I assume there is something wrong with my date variable.
let eventDate: String? = "21 Aug Sun 2016"
let eventTime: String? = "9:00 PM"
let date : String? = "\(eventDate!) \(eventTime!)"
print(date!) // "21 Aug Sun 2016 9:00 PM"
let formatter = NSDateFormatter()
formatter.dateFormat = "dd MMM eee yyyy HH:MM a"
formatter.AMSymbol = "AM"
formatter.PMSymbol = "PM"
if let dateTimeForEvent = formatter.dateFromString(date!) {
print(dateTimeForEvent)
}else {
print("Error")// prints error
}
Two things:
You have the wrong format for the time. It should be h:mm a. HH is for a two-digit, 24-hour hour. You have a 1 or 2 digit, 12-hour hour. And MM is for a 2-digit month. Use mm for a two-digit minute.
If your date and time strings will always be in English, you need to set the formatter's locale to an English locale. If you don't, your code will always return a nil date on any device using a language other than English.
Your primary issue is that you're using HH, which is for 24-hour time, instead of hh, and MM (which is for month) instead of mm. Try this:
import Foundation
let eventDate = "21 Aug Sun 2016"
let eventTime = "9:00 PM"
let eventDateTime = "\(eventDate) \(eventTime)"
print(eventDateTime) // "21 Aug Sun 2016 9:00 PM"
let formatter = NSDateFormatter()
formatter.dateFormat = "dd MMM eee yyyy hh:mm a"
if let date = formatter.dateFromString(eventDateTime) {
print(date) // 2016-08-21 21:00:00 +0000
}
else {
print("Error")// prints error, no shit? why is this comment here?
}
Side notes:
Why is a variable called date, if it's a String??
Why is date an optional, anyway? You assigned it a literal value.
You don't have to set the AMSymbol and the PMSymbol. Those only pertain to printing dates, not parsing them.