NSDate intervals for yesterday

Question

I need to filter search results based on values that were added yesterday. I have seen plenty on finding yesterday using:

NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *components = [cal components:( NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit ) fromDate:[[NSDate alloc] init]];
        [components setHour:-24];
        [components setMinute:0];
        [components setSecond:0];
        NSDate *yesterday = [cal dateByAddingComponents:components toDate:[NSDate date] options:0];
predicate = [NSPredicate predicateWithFormat:@"created_at >= %@", yesterday];

But this finds 24 hours since this exact moment in time. I need to filter yesterday as 12:01am-12:00pm. So the actual 24 hour period that was yesterday.

I'm guessing that I need to do something along the lines of: 1. Take the current date 2. Find the time from the current date to 12:01am of the same day 3. Then subtract 24 hours from that date

I feel confident I can do #3 (and #1 of course), but I'm not sure how to go about #2. I maybe over thinking it but I can't seem to grasp how to say: "Ok, it's 8:03am, I need to remove 8 hours and 2 minutes which will put me at 12:01am".

Answer 1

Start with some date of today, for example "now":

NSCalendar *cal = [NSCalendar currentCalendar];
NSDate *now = [NSDate date];

Subtract one day to get some date of yesterday:

NSDateComponents *minusOneDay = [[NSDateComponents alloc] init];
[oneDay setDay:-1];
NSDate *nowMinusOneDay = [cal dateByAddingComponents:minusOneDay toDate:now options:0];

Compute start and end date of the "day calendar unit" that contains yesterday's date:

NSDate *startOfYesterday;
NSTimeInterval lengthOfYesterday;
[cal rangeOfUnit:NSDayCalendarUnit startDate:&startOfYesterday interval:&lengthOfYesterday forDate:nowMinusOneDay];
NSDate *endOfYesterday = [startOfYesterday dateByAddingTimeInterval:lengthOfYesterday];

This should work even if a daylight savings time transition occurs between today and yesterday.

Generally one should avoid to use explicit time intervals such as "24 hours", because not every day has that length.