I am trying to get date components from a date value from an API endpoint. I need to preserve the date values as they are already adjusted for time zone. Unfortunately, I have no control over how the API returns a date value.
When I get the date value (sessionTime) from the API, it is returned as follows:
2017-12-05 08:00:00 +0000
I need to set up a local notification based on that time, however, when I try to extract components from that date object with the following code:
let notifyTime = Calendar.current.dateComponents(
[.year, .month, .day, .hour, .minute, .second], from: sessionTime)
I get this:
year: 2017 month: 12 day: 5 hour: 2 minute: 0 second: 0 isLeapMonth: false
I am six hours from GMT so it is obvious what is going on, but I wish I could prevent it and extract the date components exactly as they are. The desired output would be:
year: 2017 month: 12 day: 5 hour: 8 minute: 0 second: 0 isLeapMonth: false
Can anyone help? Thanks!
You can specify the timeZone that DateComponents uses.
Like this:
let notifyTime = Calendar.current.dateComponents(in: TimeZone.current, from: sessionTime)
Related
I am trying to implement a simple countdown timer in my test app.
I have two dates:
fromDate - which is current time that I get by Date(), e.g. 2021-08-27 11:07:34 +0000
toDate - is a future date, e.g. 2021-11-17 01:00:00 +0000
I am using DateComponents to get back the difference in days, hours, minutes and seconds.
let components = Calendar.current.dateComponents([.day, .hour, .minute, .second],
from: fromDate,
to: toDate)
Its returning me back the values for days hours minute and second 81, 12, 52, 25
The values for day, minute and second are correct, but the hour is 1 hour less.
I suspect daylight timing has to do something with this but I cannot find anything that can help here.
Kindly help me what I am doing wrong as I have tried many things in past few days but nothing seems to work
I was able to reproduce the behaviour by using:
let from = Date(timeIntervalSince1970: 1630062455)
print(from) // 2021-08-27 11:07:35 +0000
let to = Date(timeIntervalSince1970: 1637110800)
print(to) // 2021-11-17 01:00:00 +0000
var calendar = Calendar(identifier: .gregorian)
calendar.timeZone = TimeZone(identifier: "Europe/London")!
let comp = calendar.dateComponents([.day, .hour, .minute, .second], from: from, to: to)
print(comp.day!, comp.hour!, comp.minute!, comp.second!)
The reason why this happens is because when doing dateComponents(_:from:to:), Calendar takes into account its timezone. After all, without a timezone, (almost) no date components would make sense - you would not be able to tell what hour a Date is, for example. A Date just represents an instant in time/n seconds since the epoch.
(In the case of Calendar.current, the timezone it uses is TimeZone.current)
Europe/London would go out of DST at some point between from and to. This means the calendar would calculate the difference in date components between:
from: 2021-08-27 12:07:35
to: 2021-11-17 01:00:00
Notice that the first time is 12:07:35, rather than 11:07:35. This is because at 2021-08-27 11:07:35 +0000, the local date time at Europe/London really is 2021-08-27 12:07:35.
To get your desired output, just change the calendar's timeZone to UTC:
var calendar = Calendar.current
calendar.timeZone = TimeZone(identifier: "UTC")!
let comp = calendar.dateComponents([.day, .hour, .minute, .second], from: from, to: to)
Does anyone have an answer to why I am getting -8 hours instead of -7 (my timezone) hours difference upon converting time from GMT to local i using the formula below:
print("TIMEZONE IN HOURS: \(timeZone/3600)")
let interval = Date(timeIntervalSinceReferenceDate: 93866.4142533315)
print("GMT TIME: \(interval)")
let intervalDateComponents = calendar.dateComponents([.hour, .minute, .second], from: interval)
let mHour = intervalDateComponents.hour ?? 0
let mMinute = intervalDateComponents.minute ?? 0
print("INTERVAL DATE COMPONENT: \(intervalDateComponents)")
let formatter = DateFormatter()
formatter.timeZone = TimeZone.current
formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
let intervalDateString = formatter.string(from: interval)
print("DATE STRING FORMAT: \(intervalDateString)")
prints out the following: (please pay attention to date)
TIMEZONE IN HOURS: -7
GMT TIME: 2001-01-02 02:04:26 +0000 (January 2)
INTERVAL DATE COMPONENT: hour: 18 minute: 4 second: 26 isLeapMonth: false
DATE STRING FORMAT: 2001-01-01 18:04:26 (January 1)
interval HOURS: 18
edit/update:
let mDateString = formatter.string(from: interval)
print("DATE STRING FORMAT: (mDateString)")
let mdate = formatter.date(from: mDateString)
print("MDATE: (mdate)")
let mDateComponents = calendar.dateComponents([.hour, .minute, .second], from: mdate!)
print("M DATE COMPONENT: (mDateComponents)")
prints out:
DATE STRING FORMAT: 2001-01-01 19:01:27 -0700
MDATE: Optional(2001-01-02 02:01:27 +0000)
M DATE COMPONENT: hour: 18 minute: 1 second: 27 isLeapMonth: false
If you notice above in the code my intention is to extract the local time component to trigger alarm at a later time daily. So I fed the string that shows
2001-01-01 19:01:27 -0700
I converted the string to mdate in order to get time components that I need to use for the alarm to work on time so I got (hour: 18) rather than hour: 19 which I used to generate the mdate string.
The problem there is that you are getting the timezone offset for today. You need to get the timezone offset for the same date you are using:
let timeZone = TimeZone.current.secondsFromGMT(for: interval)
print("TIMEZONE IN HOURS: \(timeZone/3600)")
I am currently facing a weird issue. I am trying to find out in which week of a month a given Date instance lies.
My code is the following:
var calendar : Calendar {
var calendar = Calendar(identifier: .iso8601)
calendar.timeZone = .UTC
return calendar
}
func generateDate(year: Int, month: Int, day: Int) -> Date {
let dateComponents = DateComponents(year: year, month: month, day: day)
return calendar.date(from: dateComponents)!
}
print(calendar.component(.weekOfMonth, from: Date.generateDate(year: 2019, month: 12, day: 1))) // prints "0"
print(calendar.component(.weekOfMonth, from: Date.generateDate(year: 2020, month: 1, day: 1))) // prints "1"
generateDate simply generates a Date with the help of calendar. When I print the both statements I get 0 and 1 as the result. In my opinion this is wrong. I would assume I get the same value for both since both dates should be in the first week of their respective month value.
Another example would be the 2. Dec 2019, this should give the second week as well as the 6. January 2020 should also give me the second week.
Does anyone know what could be wrong here or where my mistake could be ?
This is due to the 1st day of the month falling on a sunday, try march 01, 2020 if you want confirmation.
The first week of the month is chosen by Swift according to their own standards as ISO standards do not suggest any specific implementations so the Swift team went with this. You can ask them in their forums what their reasoning behind this is Wikipedia link
The logic for .weekOfMonth seems to be that if the "first" week is less than half a week, that is 3 days, then it is considered to be week 0 and otherwise week 1. But note that this is dependent on what locale is being used, for a country like Canada that has Sunday as first day of week there is never a week 0 when running the below code. So when the first day of week is Monday .weekOfMonth will return a value between 0 and 5 but when it is Sunday the range is 1 to 6.
This can be seen running the following code in a playground
let calendar = Calendar.current
let year = 2019
print("First day of week: \(calendar.weekdaySymbols[calendar.firstWeekday - 1])")
for month in 1...12 {
print(calendar.monthSymbols[month - 1])
let first = calendar.date(from: DateComponents(year: year, month: month, day: 1))!
if let range = calendar.range(of: .day, in: .month, for: first) {
var currentWeek = -1
for day in range {
let date = calendar.date(from: DateComponents(year: year, month: month, day: day))!
let week = calendar.component(.weekOfMonth, from: date)
if week > currentWeek {
currentWeek = week
let dayOfWeek = calendar.component(.weekday, from: date)
print("Week# \(week), weekday \(calendar.weekdaySymbols[dayOfWeek - 1])")
}
}
}
}
It seems to me if you want whatever day it is on the 1st to be the first day of weekOfMonth = 1 then you need to write your own code for this
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
I create an instance of DateComponents using the following code:
let dateComponents = DateComponents(
calendar: .current,
timeZone: Calendar.current.timeZone,
era: nil,
year: nil,
month: nil,
day: nil,
hour: 9,
minute: 0,
second: 0,
nanosecond: 0,
weekday: 2,
weekdayOrdinal: nil,
quarter: nil,
weekOfMonth: nil,
weekOfYear: nil,
yearForWeekOfYear: nil)
I then print the dateComponents object and get the following (expected) output:
calendar: gregorian (current) timeZone: Europe/London (current) hour: 9 minute: 0 second: 0 nanosecond: 0 weekday: 2 isLeapMonth: false
Immediately following this, I print the date created using the following code:
print(Calendar.current.date(from: dateComponents)!)
To my great dismay and thorough unhappiness, the following is outputted:
0001-01-01 09:01:15 +0000
The date(from: dateComponents) function appears to have added just over a minute to the dateComponents before creating a date from them.
Thanks for any help in advance.
NSDate has some strange and undocumented behaviors for ancient dates. The change seems to have happened around 1895:
for year in 1890..<1900 {
// January 1 of each year # 9AM
let dateComponents = DateComponents(
calendar: .current,
timeZone: Calendar.current.timeZone,
year: year,
month: 1,
day: 1,
hour: 9)
if dateComponents.isValidDate {
print(dateComponents.date!)
}
}
My calendar is Gregorian and timezone is EDT (UTC -0500). This is the output:
1890-01-01 14:17:32 +0000
1891-01-01 14:17:32 +0000
1892-01-01 14:17:32 +0000
1893-01-01 14:17:32 +0000
1894-01-01 14:17:32 +0000 // not correct
1895-01-01 14:00:00 +0000 // correct
1896-01-01 14:00:00 +0000
1897-01-01 14:00:00 +0000
1898-01-01 14:00:00 +0000
1899-01-01 14:00:00 +0000
So for the years prior to 1895, Apple somehow added 17 minutes and 32 second to my time. You got a different offset, which is likely due your locale settings.
I couldn't find anything historical event about the Gregorian calendar in 1895. This question mentions that Britain started to switch over to GMT and the Greenwich Observatory started adjusting date/time standards across the British Isles in the 1890s so that may have accounted for this offset. Perhaps someone can delve into the source code for Date / NSDate and figure it out?
If you want to use DateComponent to store a repeating schedule, use nextDate(after:matching:matchingPolicy:) to find the next occurance of your schedule:
let dateComponents = DateComponents(calendar: .current, timeZone: .current, hour: 9, weekday: 2)
// 9AM of the next Monday
let nextOccurance = Calendar.current.nextDate(after: Date(), matching: dateComponents, matchingPolicy: .nextTime)!