NSGregorianCalendar ignores its timezone property

Question

In my app, I try to change the normal start & end of the day. So, I will set the start of the day to be at 04:00:00 and the end of the day to be next day at 03:59:59 and consider different timezones
My code is as following

NSDate *date = [NSDate date];
NSCalendar *gregorian = [[NSCalendar alloc]  
                                       initWithCalendarIdentifier:NSGregorianCalendar];
[gregorian setTimeZone:[NSTimeZone localTimeZone]];

NSDateComponents *comps = [gregorian  
         components:NSYearCalendarUnit|NSMonthCalendarUnit|         
        NSDayCalendarUnit|NSHourCalendarUnit|NSMinuteCalendarUnit|NSSecondCalendarUnit|
        NSTimeZoneCalendarUnit fromDate:date];
[comps setTimeZone:[NSTimeZone localTimeZone]];

// Start of Day
comps.hour = 4;
//comps.hour = 4 + ([[NSTimeZone localTimeZone] secondsFromGMT] / 60 / 60);
comps.minute = 0;
comps.second = 0;   
NSDate *startOfDay = [gregorian dateFromComponents:comps];
NSLog(@"Start of day %@", startOfDay);
//Prints Out: Start of day 2014-04-16 02:00:00 +0000

// End of Day 
comps.day = comps.day +1;
comps.second = -1;
NSDate *endOfDay = [gregorian dateFromComponents:comps];
NSLog(@"End of day %@", endOfDay);
//Prints Out: End of day 2014-04-17 01:59:59 +0000

Please, I have 3 questions:
1. Why the NSGregorianCalendar ignores setting its property timezone and I must add the timezone to the number of hours ?
2. Also, Why the timezone is not printed?
3. Is the shown code for computing end of day, good?

It's not quite clear what exactly you want to achieve. Do you want to get NSDate instances which represent beginning and the end of the day? — Yuriy Panfyorov, Apr 16 '14 at 04:03
I don't want to get the normal beginning (00:00:00) and end (23:59:59) of the day. But I want to make the beginning of the day to be at 04:00:00 and the end of the day to be at (03:59:59) next day. — user807146, Apr 16 '14 at 11:51
I'm guessing you're confused by the NSLog output. Actually, NSDate's -description always prints GMT time (which is marked by +0000 time zone offset). I think the time was calculated correctly, assuming your local time zone is GMT+2. However, If you want to format the NSDate value according to your local preferences, use NSDateFormatter. Or take a look at -descriptionWithLocale: of NSDate. — Yuriy Panfyorov, Apr 16 '14 at 18:07
Thanks, You are right for NSLog method. But what about [gregorian dateFromComponents:comps], why this method ignores the timezone I set before, and calculates the date for GMT. — user807146, Apr 18 '14 at 02:31
Take a look at the accepted answer here, it may clear things up: http://stackoverflow.com/questions/7325837/nscalendar-datefromcomponents-gmt-timezone-instead-of-systemtimezone — Yuriy Panfyorov, Apr 18 '14 at 15:52

NSGregorianCalendar ignores its timezone property

0 Answers0