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
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 thatNSDate
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 fromNSDateFormatter
'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 solutionTry adding this lines to your code,
or
SWIFT update :
Code from quetion,
And Solution ,
OR