How to calculate first NSDate of current week?

Question

i.e.:

  NSDate *firstDayOfWeek = [[NSDate date] firstDayOfWeek];

for example, today is Aug 19, I'd want to get a NSDate of 2010-08-15 12:00am from above line of code. Thanks!

Answer 1

Use NSDateComponents and set the weekday to 1.

Answer 2

I think this threads responds to what you're looking for: http://www.cocoabuilder.com/archive/cocoa/211648-nsdatecomponents-question.html#211826

Note however that it doesn't handle Mondays as first days of the week, so you may have to tweek it a little by substracting [gregorian firstWeekday] instead of just 1. Also, I modified it to use -currentCalendar, but it's up to you :-)

NSDate *today = [NSDate date];
NSCalendar *gregorian = [NSCalendar currentCalendar];

// Get the weekday component of the current date
NSDateComponents *weekdayComponents = [gregorian components:NSWeekdayCalendarUnit fromDate:today];
/*
Create a date components to represent the number of days to subtract
from the current date.
The weekday value for Sunday in the Gregorian calendar is 1, so
subtract 1 from the number
of days to subtract from the date in question.  (If today's Sunday,
subtract 0 days.)
*/
NSDateComponents *componentsToSubtract = [[NSDateComponents alloc] init];
/* Substract [gregorian firstWeekday] to handle first day of the week being something else than Sunday */
[componentsToSubtract setDay: - ([weekdayComponents weekday] - [gregorian firstWeekday])];
NSDate *beginningOfWeek = [gregorian dateByAddingComponents:componentsToSubtract toDate:today options:0];

/*
Optional step:
beginningOfWeek now has the same hour, minute, and second as the
original date (today).
To normalize to midnight, extract the year, month, and day components
and create a new date from those components.
*/
NSDateComponents *components = [gregorian components: (NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit)
                                            fromDate: beginningOfWeek];
beginningOfWeek = [gregorian dateFromComponents: components];