get NSDate from the day of the year

I have a the day of the year for example 346. I want to get NSDate to n开发者_如何学运维ow what month and day it means.

Your steps here:

• Instantiate calendar
• Build a date with 1st Jan. of the year
• Add the number of days - 1 and build a date with that
• Get the components you are interested in

Watch out if the date you get is 0- or 1-based.

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

NSDateComponents *comps = [[NSDateComponents alloc] init];
[comps setYear:theYear];
[comps setMonth:1];
[comps setDay:1];
NSDate *date = [gregorian dateFromComponents:comps];
[comps release];

NSDateComponents *compsToAdd = [[NSDateComponents alloc] init];
[comps setDay:theDay-1];

NSDate *finalDate = [gregorian dateByAddingComponents:compsToAdd date options:0];

[compsToAdd release]

NSDateComponents *interestingComponents =  [gregorian components:(NSDayCalendarUnit | NSMonthCalendarUnit) fromDate:finalDate];
NSInteger day = [interestingComponents day];
NSInteger month = [interestingComponents month];

[gregorian release];

See the -dateByAddingComponents:toDate:options: method of NSCalendar.