Get Utc Time and Local Time from Nsdate Object

Get UTC time and local time from NSDate object

The documentation says that the date method returns a new date set to the current date and time regardless of the language used.

The issue probably sits somewhere where you present the date using NSDateFormatter. NSDate is just a point on a time line. There is no time zones when talking about NSDate. I made a test.

Swift

print(NSDate())

Output: 2014-07-23 17:56:45 +0000

Objective-C

NSLog(@"%@", [NSDate date]);

Output: 2014-07-23 17:58:15 +0000

Result - No difference.

Objective-C, How can I get the current date in UTC timezone?

NSDate *currentDate = [[NSDate alloc] init];

Now it is in UTC, (at least after using the method below)

To store this time as UTC (since refernce date 1970) use

double secsUtc1970 = [[NSDate date]timeIntervalSince1970];

Set Date formatter to output local time:

NSTimeZone *timeZone = [NSTimeZone defaultTimeZone];
// or Timezone with specific name like
// [NSTimeZone timeZoneWithName:@"Europe/Riga"] (see link below)
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setTimeZone:timeZone];
[dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"];
NSString *localDateString = [dateFormatter stringFromDate:currentDate];

Available NSTimeZone names

A NSDate object always uses UTC as time reference, but the string representation of a date is not neccessarily based on UTC timezone.

Please note that UTC is not (only) a timeZone, It is a system how time on earth is measured, how it is coordinated (The C in UTC stands for coordinated).

The NSDate is related to a reference Date of midnight 1.1.1970 UTC, altough slightly wrongly described by Apple as 1.1.1970 GMT.

In the original question the last word timeZone is not perfect.

Converting UTC date format to local nsdate

Something along the following worked for me in Objective-C :

// create dateFormatter with UTC time format
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss"]; 
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"UTC"]];
NSDate *date = [dateFormatter dateFromString:@"2015-04-01T11:42:00"]; // create date from string

// change to a readable time format and change to local time zone
[dateFormatter setDateFormat:@"EEE, MMM d, yyyy - h:mm a"];
[dateFormatter setTimeZone:[NSTimeZone localTimeZone]];
NSString *timestamp = [dateFormatter stringFromDate:date];

I keep these two websites handy for converting different time formats:
http://www.w3.org/TR/NOTE-datetime

http://benscheirman.com/2010/06/dealing-with-dates-time-zones-in-objective-c/

In Swift it will be:

// create dateFormatter with UTC time format
  let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
        dateFormatter.timeZone = NSTimeZone(name: "UTC") as TimeZone?
        let date = dateFormatter.date(from: "2015-04-01T11:42:00")// create   date from string

        // change to a readable time format and change to local time zone
        dateFormatter.dateFormat = "EEE, MMM d, yyyy - h:mm a"
        dateFormatter.timeZone = NSTimeZone.local
        let timeStamp = dateFormatter.string(from: date!)

Convert UTC to local time with NSDateFormatter

The question doesn't specify the nature of what you mean by converting, exactly, but the first thing you should do, regardless of the final goal, is to correctly parse the server response using a properly configured NSDateFormatter. This requires specification of the correct format string, and the time zone must be explicitly set on the formatter or it will infer it from the local time, which would be incorrect in most cases.

Specify The Format String

Let's look at the input string provided:

20140621-061250

This uses four digits for the year, two digits (with a zero-padding) for the month, and two digits (presumably, these will be zero-padded as well) for the day. This is followed by a -, then two digits to represent the hour, 2 digits for the minute, and 2 digits for the second.

Referring to the Unicode date format standards, we can derive the format string in the following way. The four digits representing the calendar year will be replaced with yyyy in the format string. Use MM for the month, and dd for the day. Next would come the literal -. For the hours, I assume that it will be in 24 hour format as otherwise this response is ambiguous, so we use HH. Minutes are then mm and seconds ss. Concatenating the format specifiers yields the following format string, which we will use in the next step:

yyyyMMdd-HHmmss

In our program, this would look like:

NSString *dateFormat = @"yyyyMMdd-HHmmss";

Configure the input date formatter

The time format above does not specify a time zone, but because you have been provided the specification for the server response that it represents the UTC time, we can code this into our application. So, we instantiate an NSDateFormatter, set the correct time zone, and set the date format:

NSTimeZone *inputTimeZone = [NSTimeZone timeZoneWithAbbreviation:@"UTC"];
NSDateFormatter *inputDateFormatter = [[NSDateFormatter alloc] init];
[inputDateFormatter setTimeZone:inputTimeZone];
[inputDateFormatter setDateFormat:dateFormat];

Convert the input string to an NSDate

For demonstration purposes, we hard-code the string you received from the server response; you would replace this definition of inputString with the one you get from the server:

NSString *inputString = @"20140621-061250";
NSDate *date = [inputDateFormatter dateFromString:inputString];

At this point, we have the necessary object to do any further conversions or calculations - an NSDate which represents the time communicated by the server. Remember, an NSDate is just a time stamp - it has no relation to a time zone whatsoever, which only plays a role when converting to and from string representations of the date, or representations of a calendrical date via NSDateComponents.

Next steps

The question doesn't clearly specify what type of conversion is needed, so we'll see an example of formatting the date to display in the same format as the server response (although, I can't think of a likely use case for this particular bit of code, to be honest). The steps are quite similar - we specify a format string, a time zone, configure a date formatter, and then generate a string (in the specified format) from the date:

NSTimeZone *outputTimeZone = [NSTimeZone localTimeZone];
NSDateFormatter *outputDateFormatter = [[NSDateFormatter alloc] init];
[outputDateFormatter setTimeZone:outputTimeZone];
[outputDateFormatter setDateFormat:dateFormat];
NSString *outputString = [outputDateFormatter stringFromDate:date];

Since I'm in UTC-06:00, printing outputString gives the following:

20140621-001250

It's likely you'll instead want to use setDateStyle: and setTimeStyle: instead of a format string if you're displaying this date to the user, or use an NSCalendar to get an NSDateComponents instance to do arithmetic or calculations on the date. An example for displaying a verbose date string to the user:

NSTimeZone *outputTimeZone = [NSTimeZone localTimeZone];
NSDateFormatter *outputDateFormatter = [[NSDateFormatter alloc] init];
[outputDateFormatter setTimeZone:outputTimeZone];
[outputDateFormatter setDateStyle:NSDateFormatterFullStyle];
[outputDateFormatter setTimeStyle:NSDateFormatterFullStyle];
NSString *outputString = [outputDateFormatter stringFromDate:date];

Printing outputString here gives us the following:

Saturday, June 21, 2014 at 12:12:50 AM Mountain Daylight Time

Note that setting the time zone appropriately will handle transitions over daylight savings time. Changing the input string to "20141121-061250" with the formatter style code above gives us the following date to display (Note that Mountain Standard Time is UTC-7):

Thursday, November 20, 2014 at 11:12:50 PM Mountain Standard Time

Summary

Any time you get date input in a string form representing a calendar date and time, your first step is to convert it using an NSDateFormatter configured for the input's format, time zone, and possibly locale and calendar, depending on the source of the input and your requirements. This will yield an NSDate which is an unambiguous representation of a moment in time. Following the creation of that NSDate, one can format it, style it, or convert it to date components as needed for your application requirements.

Swift 3.0 : Convert server UTC time to local time and vice-versa

I don't know what's wrong with your code.
But looks too much unnecessary things are there like you're setting calendar, fetching some elements from string.
Here is my small version of UTCToLocal and localToUTC function.
But for that you need to pass string in specific format. Cause I've forcly unwrapped date objects. But you can use some guard conditions to prevent crashing your app.

func localToUTC(dateStr: String) -> String? {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "h:mm a"
    dateFormatter.calendar = Calendar.current
    dateFormatter.timeZone = TimeZone.current
    
    if let date = dateFormatter.date(from: dateStr) {
        dateFormatter.timeZone = TimeZone(abbreviation: "UTC")
        dateFormatter.dateFormat = "H:mm:ss"
    
        return dateFormatter.string(from: date)
    }
    return nil
}

func utcToLocal(dateStr: String) -> String? {
    let dateFormatter = DateFormatter()
    dateFormatter.dateFormat = "H:mm:ss"
    dateFormatter.timeZone = TimeZone(abbreviation: "UTC")
    
    if let date = dateFormatter.date(from: dateStr) {
        dateFormatter.timeZone = TimeZone.current
        dateFormatter.dateFormat = "h:mm a"
    
        return dateFormatter.string(from: date)
    }
    return nil
}

and call these function like below.

print(utcToLocal(dateStr: "13:07:00"))
print(localToUTC(dateStr: "06:40 PM"))

Hope this will help you.
Happy coding!!

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