obj-C, why does this give me yesterdays date? - iphone

Question

I've been struggling with my function to return todays date, at as close to zero seconds, minutes and hours as possible. So I'm able to re-use the same date with various transactions.
However, I've now discovered that my function returns yesterdays date?
+ (NSDate *)makeAbsoluteNSDate:(NSDate*)datSource {
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:
NSGregorianCalendar];
[calendar setTimeZone:[NSTimeZone localTimeZone]];
NSDateComponents *dateComponents = [calendar components:NSYearCalendarUnit |
NSMonthCalendarUnit | NSDayCalendarUnit
fromDate:datSource];
[dateComponents setHour:0];
[dateComponents setMinute:0];
[dateComponents setSecond:0];
NSDate *today = [calendar dateFromComponents:dateComponents];
[calendar release];
return today;
}

Answer 1

If you're trying to get today's or yesterday's midnight in your time zone, you should get NSDate that points to adequate time in GMT. In my case -2 hours as my timezone is +0200, so for midnight of 2011-08-26 I'll get 2011-08-25 22:00.
You have to make sure that you're setting the right timezone for the NSCalendar, which is [NSTimeZone systemTimeZone].
My routine for getting the midnight in my time zone is:
+ (NSDate *)midnightOfDate:(NSDate *)date {
NSCalendar *cal = [NSCalendar currentCalendar];
[cal setTimeZone:[NSTimeZone systemTimeZone]];
NSDateComponents *components = [cal components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:date];
[components setTimeZone:[cal timeZone]];
[components setHour:0];
[components setMinute:0];
[components setSecond:0];
return [cal dateFromComponents:components];
}
So, after a long discussion in comments, here's a midday function:
+ (NSDate *)middayOfDate:(NSDate *)date {
NSCalendar *cal = [NSCalendar currentCalendar];
[cal setTimeZone:[NSTimeZone systemTimeZone]];
NSDateComponents *components = [cal components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:date];
[components setTimeZone:[cal timeZone]];
[components setHour:12];
[components setMinute:0];
[components setSecond:0];
return [cal dateFromComponents:components];
}

Answer 2

Use below function to get date for yesterday :
- (NSDate *)getDate:(NSDate *)date days:(NSInteger)days hours:(NSInteger)hours mins:(NSInteger)mins seconds:(NSInteger)seconds
{
NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *components = [cal components:( NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit ) fromDate:[[NSDate alloc] init]];
days = (days*24) + hours;
[components setHour:days];
[components setMinute:mins];
[components setSecond:seconds];
NSDate *returnDate = [cal dateByAddingComponents:components toDate:date options:0];
return returnDate;
}
To get yesterday date pass date = [NSDate date], day = -1, hours = 0 and mins = 0 as parameters in method calling.

Answer 3

All you need is [NSDate date] for the current date & time.