Given a year and a week number, how do you get the date of the first day of the week?

Question

I need this for getting data in a graph for week basis. This one does not work for me. The date that it returns is first of January of the selected year. Any ideea?

-(NSDate*) getFirstDateOfTheWeek:(NSString*) weekNr andYear: (NSString*) theYear {
        int intYear = [theYear intValue];
        int intWeek = [weekNr intValue];

        NSCalendar *gregorian = [[NSCalendar alloc]
                                 initWithCalendarIdentifier:NSGregorianCalendar];
        [gregorian setLocale:[NSLocale currentLocale]];

        NSDateComponents * comp = [[NSDateComponents alloc] init];
        [comp setYear:intYear];
        [comp setWeek:intWeek];

        NSDate *dateOfFirstDay = [gregorian dateFromComponents:comp];
        NSDateComponents *dateComponents =
        [gregorian components:NSWeekdayCalendarUnit|NSWeekCalendarUnit|NSDayCalendarUnit|NSYearCalendarUnit|NSMonthCalendarUnit fromDate:dateOfFirstDay];
        int year = [dateComponents year];
        int month = [dateComponents month];
        int day = [dateComponents day];

        dateOfFirstDay= [gregorian dateFromComponents:dateComponents];
        return dateOfFirstDay;
    }

Answer 1

You should setWeekday in your NSDateComponents in addition you setYear and setWeek.

[comp setWeekday:intWeek];

Then when grabbing the new components you don't need many of the flags, as you really only need the day (and the others for debugging):

    [gregorian components:NSDayCalendarUnit|NSYearCalendarUnit|NSMonthCalendarUnit fromDate:dateOfFirstDay];