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];
}