Question

I’m looking two do two things:

1. Check if a week has gone by (based on the day of the week)
2. Check if a day has gone by (based on the date)

I’m not sure what the best way to solve this is, since when comparing two NSDates (one at 1/1/09 at 21:30 and another at 1/2/09 at 00:30) I can’t just see if 24 hours has gone by since in this case it hasn’t. I can solve this by just getting the date 1/1/09 from the NSDate, but I’m unsure how to do this based on the documentation and google links that I saw.

For the other issue, I don’t know how to know what day of the week it is given a date. I’d like to if 1/1/09 is a Tuesday, Monday, etc… Is there any library that let’s you calculate this? This obviously needs to take into account leap years and a tons of other stuff… Maybe there’s an objective-c library for this?

Thanks for any help!

Answer 1

You can use NSDateComponents for this:

unsigned units = NSYearCalendarUnit | NSMonthCalendarUnit |  NSDayCalendarUnit; NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; NSDateComponents *components = [gregorian components:units fromDate:date]; 

then you can access individual parts of the date like this:

[components year]; [components month]; [components day]; 

Or, you can construct a new NSDate object using NSCalendar‘s dateFromComponents method, and compare the two NSDate objects.