1 out error when creating NSDate from calendar components

Question

I'm trying to use the solution provided in "NSDate for first day of the month" to get the first day of month.

My code is in a NSDate category:

- (NSDate *)firstDayInMonthOfDate {
    NSCalendar* calendar = [NSCalendar currentCalendar];
    NSDateComponents *comps = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit |  NSDayCalendarUnit) fromDate:self];
    comps.timeZone = calendar.timeZone;
    NSDate *startDate;
    [comps setDay:1];
    startDate = [calendar dateFromComponents:comps];
    return startDate;
}

This yields the last day of the previous month.... example:

self = date: 2013-11-02 22:00:00  

comps = <NSDateComponents: 0x749b4c0>
        TimeZone: Europe/Bucharest (GMT+03:00) offset 10800 (Daylight)
        Calendar Year: 2013
        Month: 11
        Leap month: no
        Day: 1 

startDate = 2013-10-31 22:00:00 +0000

So, in order to get the correct day, I have to set comps.day = 2. I just don't understand where the extra 1 is coming from.

[EDIT] I want to use the dates for collection view cells, so I would like a reliable way to get the first date of the month, eg. 2013-11-01

[EDIT] Using a NSDateFormatter to print the date gives the correct result (2013-10-31). The problem with po and NSLog is that they don't interpret the timezone properly right (2012-12-31 10pm + 3h GMT != 2013-01-01 12am) I recomend a date programming tutorial: http://rypress.com/tutorials/objective-c/data-types/dates.html

***TIME ZONE*** -- This is (at least) the second time for this question with the past hour or two. And a dupe many times over. — Hot Licks, Oct 06 '13 at 12:58
If you only copy&paste code you should not be surprised, if you don't understand it. — vikingosegundo, Oct 06 '13 at 13:01
possible duplicate of [Getting date from \[NSDate date\] off by a few hours](http://stackoverflow.com/questions/8466744/getting-date-from-nsdate-date-off-by-a-few-hours) — Hot Licks, Oct 06 '13 at 13:02

score 2 · Accepted Answer · answered Oct 06 '13 at 08:03

2

Your result is correct.

NSLog(@"%@", startDate) or po startDate in the debugger always prints the date with respect to GMT, and

 startDate = 2013-10-31 22:00:00 +0000

is the same as 2013-11-01 00:00:00 in GMT+2, which is your time zone.

Note that you can simplify your code to

NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *startDate;
[calendar rangeOfUnit:NSMonthCalendarUnit startDate:&startDate
             interval:NULL forDate:self];
return startDate;

answered Oct 06 '13 at 08:03

Martin R

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Hi Martin R, thanks for your quick reply, but it's not obvious for me how to change my code. – Andrei Nagy Oct 06 '13 at 12:57
@AndreiNagy: I am fairly sure that your code is correct so far. But to get the date *displayed* according to your timezone, you have to use a NSDateFormatter. – Martin R Oct 06 '13 at 12:59
@AndreiNagy - NSLog invokes NSDate.description(), which always returns the date relative to GMT. – Hot Licks Oct 06 '13 at 13:00
Thanks for assurance, Martin R. Now I understand this subject better. – Andrei Nagy Oct 06 '13 at 14:45

1 out error when creating NSDate from calendar components

1 Answers1