how can i return a NSDate in a predefined time zone from a string
let responseString = "2015-8-17 GMT+05:30"
var dFormatter = NSDateFormatter()
dFormatter.dateFormat = "yyyy-M-dd ZZZZ"
var serverTime = dFormatter.dateFromString(responseString)
println("NSDate : \(serverTime!)")
the above code returns the time as
2015-08-16 18:30:00 +0000
The date format has to be assigned to the dateFormat property of the date formatter instead.
let date = NSDate.date()
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"
let str = dateFormatter.stringFromDate(date)
println(str)
This prints the date using the default time zone on the device. Only if you want the output according to a different time zone then you would add for example
Swift 3.*
dateFormatter.timeZone = NSTimeZone(name: "UTC")
Swift 4.*
dateFormatter.timeZone = TimeZone(abbreviation: "UTC")
also refer link http://www.brianjcoleman.com/tutorial-nsdate-in-swift/
how can i return a NSDate in a predefined time zone?
You can't.
An instance of NSDate does not carry any information about timezone or calendar. It just simply identifies one point in universal time.
You can interpret this NSDate object in whatever calendar you want. Swift's string interpolation (the last line of your example code) uses an NSDateFormatter that uses UTC (that's the "+0000" in the output).
If you want the NSDate's value as a string in the current user's calendar you have to explicitly set up a date formatter for that.
Swift 4.0
dateFormatter.timeZone = TimeZone(abbreviation: "UTC")
If you always have the same time zone for the input string, you can create two date formatters to output the local time zone (or a specified one):
let timeFormatterGet = DateFormatter()
timeFormatterGet.dateFormat = "h:mm a"
timeFormatterGet.timeZone = TimeZone(abbreviation: "PST")
let timeFormatterPrint = DateFormatter()
timeFormatterPrint.dateFormat = "h:mm a"
// timeFormatterPrint.timeZone = TimeZone(abbreviation: "EST") // if you want to specify timezone for output, otherwise leave this line blank and it will default to devices timezone
if let date = timeFormatterGet.date(from: "3:30 PM") {
print(timeFormatterPrint.string(from: date)). // "6:30 PM" if device in EST
} else {
print("There was an error decoding the string")
}
The number 1 means 1 regardless of language. Yet in English it's spelled as one, in Spanish it's una, in Arabic it wahid, etc.
Similarly 123982373 seconds pass 1970 is going to reflect differently in different timezones or calendar formats, but's all still 123982373 seconds passed 1970
The difference between 3 seconds and 7 seconds is 4 seconds. That doesn't require a calendar. Neither you need a calendar/timezone to know the difference in time between these two Epoch times 1585420200 and 1584729000
Dates are just a timeInterval from January 1, 1970 (midnight UTC/GMT). Dates also happen to have a string representation.
Repeating Nikolia's answer, Swift's default string interpolation (2015-08-16 18:30:00 +0000) uses a DateFormatter that uses UTC (that's the "+0000" in the output).
Calendars with the use of timezones give us a contextual representation that is just easier to understand than trying to calculate the difference between two gigantic numbers.
Meaning a single date (think of a single timeInterval since 1970) will have a different string interpretations per calendar. On top of that a calendar will itself vary based on time zones
I highly recommend that you go and play around with this Epoch converter site and see how selecting a different timezone will cause the string representations for the same moment/date/timeInterval to change
I also recommend to see this answer. Mainly this part:
Timezone is just an amendment to the timestamp string, it's not considered by the date formatter.
To consider the time zone you have to set the timeZone of the formatter
dateFormatter.timeZone = TimeZone(secondsFromGMT: -14400)
Related
So I have a time that's in string format HH:mm:ss (08:30:00 for example). I want to be able to convert it to 8:30 AM.
Normally it would be easy if I had the year,month,day to go along so it would be simple to do the conversions but in this case I don't need it.
My original plan was to get current Date() then assign the time to it then convert it to the new format of H:mm a but I haven't been able to do this successfully. Meaning I have only been able to convert it to a Date object that has year 1/1/2000 and the time is set in UTC.
Am I overthinking this? Is there an easier way without doing any conversions? I just want to be able to display the time in H:mm a format without altering any timezones.
You need to create a Date with the specified time value. For this, I'd simple create a new instance of Date and then use Calendar to set the time to the desired value
var date = Date()
let cal = Calendar.current
// Please note, this returns an optional, you will need to deal
// with, for demonstration purposes, I've forced unwrapped it
date = cal.date(bySettingHour: 8, minute: 30, second: 0, of: date)!
From there, you make use of a DateFormatter to format the result to a String
let formatter = DateFormatter()
formatter.dateFormat = "hh:mm a"
formatter.string(from: date)
Now, if you're starting with a String value (of HH:mm:ss), you can actually use a DateFormatter to parse it, for example...
let value = "08:30:00"
let parser = DateFormatter()
parser.dateFormat = "HH:mm:ss"
// Again, this is forced unwrapped for demonstration purposes
let parsedDate = parser.date(from: value)!
In swift, the current time Date() is retrieved from the system time of iPhone. Using DateFormatter() seems to work the same way with a given string. For example, using the following method, we can get the same result as calling Date() right when the iPhone time reaches 2018/04/01 02:00:00
let MY_DATE_STRING = "2018/04/01 02:00:00"
var resultTime: Date {
let formatter = DateFormatter()
formatter.dateFormat = "yyyy/MM/dd HH:mm:ss"
formatter.timeZone = TimeZone.current
return formatter.date(from: MY_DATE_STRING)!
}
My question is, let's say, if 2018/04/01 2:00:00 is the end of daylight saving time, so the iPhone will have two 2am on that day -- one is with DST, while the other is not. These two times should have different UTC timestamp though. If currently the iPhone(or my self-defined MY_DATE_STRING) just enters the second 2am, which is a non-DST one, how could I set the TimeZone or other attributes so that the Date() or the given MY_DATE_STRING could generate the timestamp of second 2am instead of the first one?
Following piece of code in Swift to generate time stamp of current time, but sometime it gives wrong output like different Year 2016 instead of 2015.
let todaysDate: NSDate = NSDate()
let dateFormatter:NSDateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss.SSS"
var currentTimeStamp = dateFormatter.stringFromDate(todaysDate)
print("** Current time stamp: " + currentTimeStamp)
I don't understand why does same piece of code give different output?
This was fixed for me by changing YYYY to yyyy as suggested by BhavukJain in the comments.
From https://8mobile.wordpress.com/2015/05/28/nsdateformatter-nsdate-wrong-year/
y = Year, normally the length specifies the padding, but for two letters it also specifies the maximum length.
Y = Year (in “Week of Year” based calendars), this year designation is used in ISO year-week calendar as defined by ISO 8601, but can be used in non-Gregorian based calendar systems where week date processing is desired. May not always be the same value as calendar year.
I generate a NSDate object from string.
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
dateFormatter.timeZone = NSTimeZone(abbreviation: "GMT")
let stringToDate = dateFormatter.dateFromString(dateFromService) // 2015-07-20 12:00:43 +0000
I get this string value from webserver. I need to modify for personal device timezone. Want to add hours this stringToDate object but not work
var addHours : Int = 2 // 2 hours will be added
var newDate = stringToDate.dateByAddingTimeInterval(addHours)
Use NSCalendarComponents:
let calendar = NSCalendar.currentCalendar()
let newDate = calendar.dateByAddingUnit(
.CalendarUnitHour, // adding hours
value: 2, // adding two hours
toDate: oldDate,
options: .allZeros
)
Using NSCalendar will account for things like leap seconds, leap hours, etc.
But as Duncan C's answer points out, simply adding hours is definitely the wrong approach. Two time zones won't always be separated by the same amount of time. Again, this is something especially true when we take daylight savings into account. (For example, the United States doesn't start/end daylight savings on the same days as Europe, and Arizona doesn't even do daylight savings).
You're asking the wrong question. This is what's known as an "XY Problem".
You should be asking "How do I display a date string I get from a web server in the user's local time zone."
NSDate represents a date/time in an abstract form that does not contain a time zone. You convert it to a specific time zone for display. Do not try to add/subtract hours to an NSDate to offset for time zones. That is the wrong approach.
The correct answer is simple. Create a second date formatter and don't set it's timezone to GMT. It defaults to the user's local time zone.
let dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
dateFormatter.timeZone = NSTimeZone(abbreviation: "GMT")
let date = dateFormatter.dateFromString(dateFromService)
let outputDatedateFormatter = NSDateFormatter()
outputDatedateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
//leave the time zone at the default (user's time zone)
let displayString = outputDateFormatter.stringFromDate(date)
println("Date in local time zone = \(displayString)")
For Swift 3 you can use this function:
//get next date by adding hours func
getNewDateAfterAddingHours(hoursToAdd:NSInteger, oldDate:Date) -> Int64 {
let calendar = Calendar.current
let newDate = calendar.date(byAdding: .hour, value: hoursToAdd, to: oldDate)
return Int64((newDate?.timeIntervalSince1970)!)
}
If you are doing it more often, check out library called SwiftMoment (inspired by the same .js library), which allows you to do following (and much more!):
// Create date using moment library
let myDate = moment(myString)
// Add one hour
let dateWithAddedHour = myDate + 1.hours
Moment is a wrapper around NSDate instance, while Duration (which is what you get from Int.hours, Int.minutes etc.) wraps an NSTimeInterval value.
Implementing this should take you just a moment! (Pun intended).
I am updating the question to be more precise, thank you for the feedback already.
So I am setting a cell for a tableview and displaying the time of the event on the cell itself and to do so am using Parse. The date is downloading correctly from parse as evidenced by the first println, but when I make the label text equal the dateToString of the when date (which is the one from parse) it throws it off by several hours for some reason. The simulator however displays the right time on the status bar and the phones gps is set to EST as well... So I am very confused.
Here is the entire function:
func configureCell(object : PFObject)-> Void {
eventNameText.text = (object.objectForKey("name") as? String)!
var when = (object.objectForKey("when") as? NSDate)!
numEchoesText.text = String(stringInterpolationSegment: object.objectForKey("numEchoes")!)
println(when)
var formatter = NSDateFormatter()
formatter.dateFormat = "EEEE, h:mm a"
parseid = object.objectId!
if (contains(echoes, parseid)) {
echoImage.setImage(imageEchoed, forState: .Normal)
}
else {
echoImage.setImage(imageUnechoed, forState: .Normal)
}
var now = NSDate()
whenText.text = formatter.stringFromDate(when)
println(formatter.stringFromDate(now))
println(formatter.stringFromDate(when))
self.object = object
}
And here is the result:
2015-05-31 23:43:00 +0000
Tuesday, 9:30 AM
Sunday, 7:43 PM
Please note that the first time is correct but the datetostring is interpreting it as the third line. I added a middle println to display the current date in order to show that the datetostring is working correctly for the now date.
Thanks in advance for any help!!
Edit: updated answer based on new details.
Your trouble is because of the timezone. NSDate does not store any time zone information.
println(when)
--> 2015-05-31 23:43:00 +0000 // notice the timezone is 0000 / GMT
Adding a timezone to the NSDateFormatter will help you see what's going on behind the scene:
var formatter = NSDateFormatter()
formatter.dateFormat = "EEEE, h:mm a z"
println(formatter.stringFromDate(when))
--> Sunday, 7:43 PM xyz // Depends on the timezone on your device
The two represents the same point in time, but expressed in different timezones. To solve this, you need to set the timezone of the formatter to GMT:
var formatter = NSDateFormatter()
formatter.dateFormat = "EEEE, h:mm a z"
formatter.timeZone = NSTimeZone.init(name:"GMT")
println(formatter.stringFromDate(when))
--> Sunday, 11:43 PM GMT
You can remove the timezone identifier now that you get it correct. Date & time manipulation in Cocoa / iOS are a lot more complicated than other languages (Java, C#, Javascript, etc.) Sometimes I wish Apple just created a NSDate class with methods to add & subtract date/time components, switch timezone, etc. I can dream on.
Take a look at NSDateFormatter and how it works. If I do understand your question clearly, I think this should work.
var dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd hh:mm"
dateFormatter.stringFromDate(parseDateObject)
2015-05-31 23:43:00 +0000 means "the 31st of May 2015 at 23:43:00 at +0000 from UTC".
According to your question "The simulator however displays the right time on the status bar and the phones gps is set to EST".
If you convert that date from UTC to EST you get "Sunday, 7:43 PM".
Your NSDate is therefore being interpreted perfectly.
Making reasonable assumptions about the Parse API, it looks like somebody has imported your data incorrectly.