I have an ASP.NET MVC 3 website that communicates with my iOS app via JSON. As part of the objects sent in the JSON response, I have dates in the format of yyyy-MM-dd HH:mm:ss ZZZ which outputs 2011-04-05 16:28:22 -07:00. How do I parse that in iOS?
This is the code I'm messing around with right now:
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"yyyy-MM-dd'T'HH:mm:ssZZZ"];
[dateFormatter setTimeZone:[NSTimeZone localTimeZone]];
NSDate *date = [dateFormatter dateFromString:#"2011-04-05T16:28:22-0700"];
NSLog(#"%#; %#; %#", dateFormatter, date, [NSTimeZone localTimeZone]);
First thing to note is that 2011-04-05 16:28:22 -07:00 has to look like 2011-04-05T16:28:22-0700, where a T replaces the first space (assuming that stands for time, or where the time part of the string starts from?), the second space is removed and the colon in the time zone is removed. I figure I'll find a way to format the string that .NET is sending back to conform to the string iOS will parse.
The real issue is that the date that is outputted is 7 hours ahead of what I've sent in the JSON response. So, iOS outputs 2011-04-05 16:28:22 -07:00 as 2011-04-05 23:28:22 +0000, and that is wrong as far as my app is concerned.
The only solution I've found so far is to send the date in the JSON as 2011-04-05 16:28:22 +00:00, but that again is wrong because I'm altering what the real date should be.
Anyway, I'd appreciate someone taking a look and letting me know how I can parse the date string .NET is outputting via the format yyyy-MM-dd HH:mm:ss ZZZ (which I suppose can be re-written to yyyy-MM-ddTHH:mm:ssZZZ) to an NSDate object I can use in iOS.
I don't know how right this is, but I ultimately found that in .NET I have to do DateTime.ToUniversalTime().ToString("yyyy-MM-ddHH:mm:ss") and on the iOS side I have to do this:
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:#"UTC"]];
[dateFormatter setDateFormat:#"yyyy-MM-ddHH:mm:ss"];
NSDate *date = [dateFormatter dateFromString:#"2011-04-0600:28:27"];
Only then is the date correct when NSLog outputs, so I'm assuming that I've finally got a proper date/time.
Your iOS date parsing code is correct: 2011-04-05 16:28:22 -07:00 and 2011-04-05 23:28:22 +0000 represent the same time, just in different time zones. Your only problem is that NSDate doesn't actually store the time zone, and so [date description] outputs using UTC.
You're almost certainly better off just using UTC time everywhere for interchange and not bothering with time zones. I'm sure you can get that your ASP.NET code to do that, and it's easier to parse on the receiving end as well. NSDateFormatter uses standard Unicode date formatting syntax, which you can read about here.
Related
I am playing about with some timezone calculations and I have noticed quite an annoying error which is causing me problems.
If I create a date, use NSDateformatter to convert it to a certain time zone, retrieve that string, and then use dateformatter to convert the string back into a date object, it keeps reverting to my local GMT time.
Example
NSDate *date = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"yyyy-MM-dd HH:mm:ss zzz"];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:#"COT"]];
NSString *str = [dateFormatter stringFromDate:date];
NSLog(#"%#", str);
//prints 2015-02-04 10:33:45 GMT-5
NSDate *newDate = [dateFormatter dateFromString:str];
NSLog(#"%#", newDate);
//Prints 2015-02-04 15:33:45 +0000
Why does it keep reverting back to GMT? I need that date object to accurately reflect the time zone I have set the dateformatter to for some testing purposes, so this is quite a frustrating issue.
Any help would be much appreciated
I believe that the problem is that NSDate itself (i.e. the value you're logging at the end) doesn't have a time zone - it's just a moment in time. You're specifying the time zone *when formatting the value using stringFromDate*, and you're still using that when you *parse* the value back to anNSDate... but theNSDate` value itself doesn't remember the time zone.
To give a different example, imagine you had an IntegerFormatter for NSInteger, which let you say whether you wanted to format and parse in hex or decimal. You could format the decimal value 16 to 0x10, and then parse that value back... but the NSInteger wouldn't "remember" that it was parsed from hex. It's exactly the same here - the time zone plays a part in the parsing (at least when the value itself doesn't specify the time zone) but it isn't part of the result in itself.
I need that date object to accurately reflect the time zone
Then you need to keep the time zone separately alongside the NSDate, basically... (Looking at the documentation, it sounds like NSCalendarDate did what you want, but that's deprecated.)
My date is in the format
2013-07-16T07:40:36.939-04:00
When I convert it into a NSDate
the date is in the format IST or GMT +5:30 as I am in India. How should I make it use -4:00 as the timezone and display EST or PDT as per the number. if I use zzz, it returns GTM+5:30 and zzzz returns Indian Standard Time. This is my way
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"yyyy-MM-dd'T'HH:mm:ss.SSSzzz"];
NSDate *date = [dateFormatter dateFromString:strDate];
You need to set the formatted locale to en_US_POSIX to force it to use the supplied timezone instead of the system timezone:
[dateFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"]];
You're parsing the date string correctly (in iOS 6 and later; this is not date format recognized in iOS 5 which recognizes -0400 or GMT-04:00, but not -04:00). Unfortunately, NSDate objects do not have a "time zone", so that information is not captured by the NSDateFormatter.
If you really want to capture the original timezone, I think you may have to manually parse the string for those last few characters (the -04:00), determine the timezone offset from that, and store this in a separate field and when outputting the date, use this separate time zone offset to set the timeZone property of your date formatter accordingly. Or if you really want to represent the original date, you could reformat this ISO8601 date string as human-friendly string and keep this pretty string (as well as the NSDate object, presumably).
BTW, splitting hairs, but you might want to be wary about assuming that -04:00 will represent EDT because (a) it depends upon the time of the year; and (b) there are other timezones that are also -04:00 (e.g. there are a bunch of South American timezones that are also -04:00).
Generally apps avoid this problem altogether by (a) converting the date strings to NSDate objects; and (b) output these NSDate objects using the timezone and locale of the device that the app is running on.
This question already has answers here:
Get NSDate from NSDate adjusted with timezone
(2 answers)
Closed 9 years ago.
I am trying to use NSDateFormatter in my app which takes a date string and formats it to an NSDate so that I can do Date Comparisons, however I am finding when I use dateFromString and format it the date is losing one day.
NSString *dateString = #"02-06-2012";
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"dd-MM-yyyy"];
NSDate *dateFromString = [[NSDate alloc] init];
dateFromString = [dateFormatter dateFromString:dateString];
NSLog(#"My Date = %#", dateFromString);
[dateFormatter release];
This outputs to the console:
My Date = 2012-06-01 23:00:00 +0000
Try adding this lines to your code,
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:#"GMT+0:00"]];
or
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:#"GMT"]];
SWIFT update :
Code from quetion,
let dateString = "02-06-2012"
var dateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "dd-MM-yyyy"
var dateFromString : NSDate = dateFormatter.dateFromString(dateString)!
println("My Date \(dateFromString)")
And Solution ,
dateFormatter.timeZone = NSTimeZone(name: "GMT")
OR
dateFormatter.timeZone = NSTimeZone(abbreviation: "GMT+0:00")
I don't believe that Dhruv's answer is correct. In fact, it's not clear there's any problem at all. You just seem to have an incorrect expectation of what should happen and/or interpretation of what's happening.
NSDate represents a moment in time. This moment does not have one unique name. It will be known by different names in different places and under different naming systems (time zones, calendars). NSDate doesn't deal with any of this, except lamely in its -description method, where it has to produce a string representation of that moment.
Second, a string like "02-06-2012" doesn't specify a precise moment in time. First of all, it's just a date with no time information, so NSDateFormatter just defaults to the first moment for that date. Second, it doesn't specify the time zone. The first moment of the calendar day is a different moment in each time zone. Unless you specify a time zone with -setTimeZone: or the string itself carries time zone information, NSDateFormatter assumes that any date strings you ask it to parse are in the current time zone.
So, your dateFromString object represents the first moment of the specified date, 02-06-2012, in your time zone. I expect this is what you wanted. However, you then got confused by the way that NSDate describes itself when logged. As I said, NSDate has to pick some "name" (string representation) for the moment it represents and which name it picks is fairly arbitrary. These days it is picking the name that the moment is known by in UTC. I gather from the log output shown in your question that you are located at UTC+0100. So, the date may look like it's one day earlier but it really is the same moment you specified. In other words, "2012-06-01 23:00:00 +0000" and "2012-06-02 00:00:00 +0100" are two equivalent names for exactly the same moment in time. You just aren't used to seeing the first one and misinterpreted it.
The lesson is that you have to stop relying on NSDate's self-description to be in any particular time zone. Really, you have to not rely on anything about it, since it's not documented. In fact, the docs for -[NSDate description] state, "The representation is not guaranteed to remain constant across different releases of the operating system."
Dhruv's solution seems to help merely because it causes NSDateFormatter and -[NSDate description] to agree on the time zone. But that's unreliable. It wouldn't work on Snow Leopard, for example, because -[NSDate description] used the local time zone instead of UTC in that version of the frameworks.
More importantly, though, it alters the actual moment represented by the NSDate object you get from NSDateFormatter's interpretation of your date string. I suspect you really want that to have a specific meaning – you want the string to be interpreted as being in the local time zone – and his solution thwarts your intent.
tl;dr: you were getting the date you wanted all along; don't rely on -[NSDate description]; don't use Dhruv's solution
I am trying to format a date object and I am noticing on the string I am passing in; 6 hours is being added to my time. This seems to be associating my date time object to GMT.
My code:
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:#"yyyy-MM-dd h:mm:ss a"];
[formatter setTimeZone:[NSTimeZone systemTimeZone]];
NSDate *date = [formatter dateFromString:#"2012-02-01 03:38:12 AM"];
NSLog(#"%#", date);
The result is:
2012-02-01 09:38:12 +0000
I have tried this with and without the setTimeZone and it does not matter. Any ideas on why this is displaying as GMT time?
Thanks,
Flea
The date that your formatter creates is not associated with any timezone, but the description method of NSDate (which is what NSLog uses for the output) converts any date to UTC. You would have to use another (or the same) date formatter's stringFromDate: method to print it with a different time zone.
All NSDates are absolute times, meaning that 3:00 AM central time in the United States is 9 AM UTC. I suspect that your systemTimeZone is central time in the United States.
NSLog always shows times in UTC.
If you want to see, as a string, what the time is in your time zone, then you can use the same date formatter stringFromDate: method, and make the you set the time zone of the date formatter to that time zone.
NSLog date formatting is an annoyance because it leads to the kind of confusion you are experiencing.
Before Xcode 4 I used to use NSDate initFromString but it is now deprecated and produces errors in Xcode 4.2. So I jumped over to using NSDateFormatter dateFromString but ran into an issue in a method I call that gets a sunrise date from string and a sunset date from string to determine if it is day or night (so same method). The first call works fine, but the second call returns nil. I decided to see if it was repeatable so I created the following simple method and dumped it into another project in an innocuous place:
- (void)testDateFormatter
{
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat: #"yyyy-MM-dd hh:mm:ss Z"];
NSString *srDateTimeString = #"2011-11-09 07:08:00 -0800";
NSString *ssDateTimeString = #"2011-11-09 17:08:00 -0800";
NSDate *sunriseDateTime = [formatter dateFromString: srDateTimeString];
NSDate *sunsetDateTime = [formatter dateFromString: ssDateTimeString];
return;
}
The first call returns the correct date. The second call returns nil. I have tried several variations (such as creating two separate NSDateFormatters, preinitializing the dates, preinitializing the dates to the current time and then reassigning) but none do the expected thing.
Does anyone know what is going on here? Since I hadn't found any reference to this error anywhere I submitted it to Apple (bug #10420498).
Jack
In the second string, the hour is 17 (24-hour format) but the format string uses hh (lowercase) which is for 12-hour format.
Change the format string to yyyy-MM-dd HH:mm:ss Z.
In the documentation, see Date Formatters which contains a link to the Unicode Date Format Patterns listing each format specifier.