Working with NSCalendar — getting the next first tuesday of a month

Question

This is a bit odd, but is it possible to use an NSCalendar (or any component, for that matter) to figure out what the date of the next "first tuesday of the month" would be?

For example, today is Thursday March 25, 2010. The next "first tuesday of the month" would be on April 6. Likewise, if I were looking for the next "first tuesday of the month" on April 1, it would still be on April 6.

How would you do this?

Thanks very much!!!!!

Answer 1

The code below calculates the first Tuesday of a given month/year combination. It's written in MacRuby because that is what I just tried it with, but you should have no problems to convert it to proper Objective-C, it's just a different syntax (I love MacRuby for quickly trying out an idea):

dc = NSDateComponents.alloc.init
# Set month to April 2010
dc.setYear 2010
dc.setMonth 4

dc.setWeekday 3 # 1 = Sunday, 2 = Monday, ...
dc.setWeekdayOrdinal 1 # We want the first weekday of the month

cal = NSCalendar.alloc.initWithCalendarIdentifier NSGregorianCalendar
date = cal.dateFromComponents dc
date.description # => "2010-04-06 00:00:00 +0200"

I leave it to you to determine the "next first Tuesday" from a given date: do the calculation for the month of the current date first and if the result is in the past, do it again for the following month. Use -[NSCalendar components:fromDate:] to get the month/day combo of a given NSDate.

Answer 2

Unfortunately I can not verify the incapacity of this code, but some should look like this:

NSDateComponents *components = [[NSDateComponents alloc] init];
[components setWeekday:2]; // Monday
[components setMonth:5]; // May
[components setYear:2008];
[components setWeekdayOrdinal:1]
NSCalendar *gregorian = [[NSCalendar alloc]
                         initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *date = [gregorian dateFromComponents:components];

For samples and detail info see this guide