Swift date components incorrect return of date day number - swift

I need to obtain a date from some variable values
So I specify year, month and day and I need a Date as return
Doing the following works except for the day because it return the day input - 1
let todayDate: Date = Calendar.current.startOfDay(for: Date.from(year: 2022, month: 09, day: 05)!)
print("today date = \(todayDate)")
extension Date {
static func from(year: Int, month: Int, day: Int) -> Date? {
let calendar = Calendar(identifier: .gregorian)
var dateComponents = DateComponents()
dateComponents.year = year
dateComponents.month = month
dateComponents.day = day
return calendar.date(from: dateComponents) ?? nil
}
}
And the output is
today date = 2022-09-04 22:00:00 +0000

Date and time can be a bit tricky. The Date struct stores a point in time relative to GMT. If you print it it will show exactly that.
Solution:
Don´t use print, use a proper Dateformatter. To illustrate what I mean use this in a playground:
let date = Calendar.current.startOfDay(for: Date())
print(date)
//2022-09-03 22:00:00 +0000
// when it is 4.th of september 00:00 in my timezone (+- Daylight saving) it is this time in GMT
let formatter = DateFormatter()
formatter.dateFormat = "dd MM yyyy HH:mm:ss"
print(formatter.string(from: date))
//04 09 2022 00:00:00
// this is the time in my timezone
So the issue here is not that it has the wrong time, it is just not presented in the correct time zone.

Related

ISO8601dateformatter 1970-01-01 00:00:00 issue

How to deal with the new year and ISO8601 returning last year as year component.
To my horror, I realized ISO8601DateFormatter was returning 1977 as a year to the 1978-01-01 00:00:00
It took a while to realize this. That turned out is not wrong. Nonetheless, given the specific year of 1978, for the formatted to return 1977 is shocking.
I don't even need the timestamp. How can I reliably retrieve the specified year without having to add a second to every calendar date?
import Foundation
let datestring = "1978/1/1"
var formatter = ISO8601DateFormatter()
formatter.timeZone = TimeZone(abbreviation: "UTC")
formatter.formatOptions = [.withFullDate]
let date2 = formatter.date(from: datestring) ?? Date()
print(date2)
var calendar = Calendar(identifier: .iso8601)
var year = calendar.component(.year, from: date2)
var month = calendar.component(.month, from: date2)
var day = calendar.component(.day, from: date2)
var era = calendar.component(.era, from: date2)
print("year \(year) month \(month) day \(day) era: \(era)")
===
1978-01-01 00:00:00 +0000
year 1977 month 12 day 31 era: 1
By default the Calendar instance will have your local timeZone. You can see this by printing print(calendar.timeZone.abbreviation() ?? "UNKNOWN"). In my case (in Seattle, WA, USA) it prints "PDT". If you simply set your calendar timezone to UTC it prints exactly what you expect:
year 1978 month 1 day 1 era: 1

In Swift, how to delete hours in a Date object?

i need to use a dictionary of dates, and i need to delete all the information about a date except:
day
month
year
i create this static function:
let day = Date() // it's an example
print(day)
func dateSimplificator(WithDate date: Date) -> Date {
let formatterD = DateFormatter()
formatterD.dateFormat = "dd MM yyyy"
let dayString = formatterD.string(from: date)
let reFormatterD = DateFormatter()
reFormatterD.dateFormat = "dd MM yyyy"
let dayFormatted = reFormatterD.date(from: dayString)!
//print(dayFormatted)
return dayFormatted
}
print(dateSimplificator(WithDate: day))
and when i print, i obtain:
2020-09-03 10:40:25 +0000
2020-09-02 23:00:00 +0000
it isn't what i want.
I need somthing like this:
the date => 2020-09-03 10:40:25 +0000
and when i use the static function with the date, i have to obtain a new date like this :
2020-09-02 00:00:00 +0000
what should a change in my function?
First of all your method can be written without a date formatter
func dateSimplificator(with date: Date) -> Date {
return Calendar.current.startOfDay(for: date)
}
Second of all a date formatter considers the local time zone – which is clearly UTC+0100 in your case – but print shows dates in UTC. 2020-09-03 00:00:00 +0100 and 2020-09-02 23:00:00 +0000 is the same moment in time.

Swift Calendar.current.nextDate timeZone issues

I am trying to get a Date object for the next occurring future time where the hour in UTC time is 18. However my code doesn't work as expected. I have the following:
let dateComponents = DateComponents(timeZone: TimeZone(abbreviation: "GMT"), hour: 18)
let date = Calendar.current.nextDate(after: Date(), matching: dateComponents, matchingPolicy: .nextTime)
print(date)
The problem is that this results in 2019-02-09 23:00:00 +0000
The date is for the next occurring time where the hour is 18 in EST.
I would have expected, since the the dateComponents has the timezone set to UTC and the hour to 18, that the date would be 2019-02-09 18:00:00 +0000. Furthermore, changing the timezone seems to have no effect on the nextDate found.
Why doesn't the nextDate function respect the timezone set in the dateComponents passed to it?
It looks like the timezone in DateComponents is ignored.
However when you set the timezone in a new calendar you get correct results.
let dateComponents = DateComponents(hour: 18)
var calendar = Calendar(identifier: .gregorian)
calendar.timeZone = TimeZone(secondsFromGMT: 0)!
let date = calendar.nextDate(after: Date(), matching: dateComponents, matchingPolicy: .nextTime)
print(date) // Optional(2020-09-29 18:00:00 +0000)
I live in GMT time, and running this in a playground produces the expected result you are looking for. You are setting the time zone of your date component, but I would imagine your own calendar (Calendar.current) is set to EST. You would need to account for the offset in EST vs GMT for your required result

Swift date manipulation - strange month return

I'm trying to do some date manipulation with Swift and I'm getting an unexpected result. The webservice will pass in a string date, and then I want to get that month and the previous month. I'm using this code (with input grab and such removed):
import Foundation
let formatter = DateFormatter()
formatter.locale = Locale(identifier: "en_US_POSIX")
formatter.timeZone = TimeZone(identifier: "America/New_York")
formatter.dateFormat = "yyyy-MM-dd"
let date = formatter.date(from: "2018-12-01")!
let prev = Calendar.current.date(byAdding: .month, value: -1, to: date)!
formatter.string(from: date)
formatter.string(from: prev)
So I've got a valid date, and then I subtract a month from it. The first formatted date shows my expected 2018-12-01 but then on the second line, instead of saying 2018-11-01 it says 2018-10-31.
I'm in PST, which is of course 3 hours ahead of EST. If I add 3 hours I'd get the expected strings. However, since both the input and the output strings were done with a formatter using the timezone, why don't I get the expected output?
The problem is that Calendar.current is in a different timezone (for you) than the formatter.
So date is December 1, 2018 at midnight New York time. But that is November 30, 2018 at 9pm local time (PST) for you.
When you subtract one month it is done in local time (Calendar.current) so you get October 30, 2018 at 9pm. Then you format that date to New York time and it results in October 31, 2018 at midnight.
To get the proper results you want a Calendar in the same timezone as the formatter:
var cal = Calendar(identifier: Calendar.current.identifier)
cal.timeZone = formatter.timeZone
let prev = cal.date(byAdding: .month, value: -1, to: date)!
This will give the expected result.

storing date in coredata swift

I have a textfield connected to a date picker
I am then trying to store the selected date into core data,
My log off the date picked by the user seems ok:
2016-01-29 00:00:00 +0000 [I strip the time component with some code]
This is converted into a String and displayed in the textfield called startDate.
func handleDatePicker(sender: UIDatePicker) {
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "EEE, dd MMM YYYY"
startDate.text = dateFormatter.stringFromDate(sender.date)
}
Now the strange thing is that when I try and store this into CoreData and convert the string back into a date (the attribute I am saving it into is configured as a Date)
let cont = self.context
let newCustomer = NSEntityDescription.entityForName("Customer", inManagedObjectContext: cont)
let aCust = Customer(entity: newCustomer!, insertIntoManagedObjectContext: cont)
let DF = NSDateFormatter()
DF.dateFormat = "EEE, dd MMM YYYY"
aCust.c15das = DF.dateFromString(startDate.text!)
print("Saved Date: \(DF.dateFromString(startDate.text!))")
Now the log prints out:
2015-12-25 00:00:00 +0000
Why the difference? How can I stop this happening?
Sorry if its something obvious that I am not spotting.
"EEE, dd MMM YYYY" -> YYYY: "Week of Year Calendar", aka "ISO Week Date System". The first week does not start on the first January. If the January 1st is either Monday, Tuesday, Wednesday or Thursday, the whole week is the first week of the new year. if it is Friday, Saturday or Sunday the week is the 53rd week of the last year. So this is a calendar with year that only have integral weeks. Either 52 or 53, rather than 365 or 366 days.
In this calendar January 29th would be the 5th day of the 4th week of the year 2016 — 2016-W4-5. This system does not know months and therefor your date is nonsense.
You want "EEE, dd MMM yyyy", as yyyy indicates a year that starts on 1st of January and ends after 31st of December — The Gregorian Year.
[I strip the time component with some code]
You shouldn't do that. Rather NSCalendar's method to get a date at the beginning of the day.
var today: NSDate?
cal.rangeOfUnit(.Day, startDate: &today, interval: nil, forDate: date)
Try this code, that worked for me:
let dateString = "Fri, 29 Jan 2016" // change to your date format
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "EEE, dd MMM yyyy"
dateFormatter.timeZone = NSTimeZone(name: "UTC")
let date = dateFormatter.dateFromString(dateString)
print(date!)