Re: Finding a relative date

FROM : Nick Zitzmann
DATE : Mon Feb 25 20:57:35 2008

On Feb 25, 2008, at 12:27 PM, Randall Meadows wrote:

> Given a specific NSDate, I need to be able to find, say, the Sunday 
> before that date, or the Saturday after that date.  I was hoping to 
> be able to use +dateWithNaturalLanguage with something like "Sunday 
> before [myDate description]", but that just returns myDate.
>
> I know I can brute-force it, by figuring out the myDate's day, then 
> walking backward and/or forward, but is there an easier way?  One 
> more tried and true, less error-prone, that's calendar-savvy (not 
> that I'm going to need to go as far back as Oct 1582...)?



You can do this with NSCalendar, doing something like this: (warning, 
written in Mail, untested, use at your own risk, etc.)

NSCalendar *cal;    // initialize this
NSDate *date;        // initialize this
NSDate *dateLastSunday;
NSInteger weekday;
NSDateComponents *addComponents = [[[NSDateComponents alloc] init] 
autorelease];

weekday = [[cal components:NSWeekdayCalendarUnit fromDate:date] 
weekday];
if (weekday == 1)    // Sunday
   [addDateComponents setDay:-7];
else            // Monday-Saturday
   [addDateComponents setDay:(weekday-1)*-1];
dateLastSunday = [cal dateByAddingComponents:addDateComponents 
toDate:date options:0];

Nick Zitzmann
<http://www.chronosnet.com/>