How do I calculate the number of days in this year in Objective C

Question

How can i calculate the number of days in a year for any calendar, not just gregorian. I have tried this

NSUInteger *days = [[NSCalendar currentCalendar] rangeOfUnit:NSDayCalendarUnit inUnit:NSYearCalendarUnit forDate:[NSDate date]];

but that gives me the number of days in the current month instead of the number of days in the current year.

Answer 1

I finally came up with a solution that works. What I do is first calculate the number of months in the year and then for each month calculate the number of days for that month.

The code looks like this:

NSUInteger days = 0;
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *today = [NSDate date];
NSDateComponents *components = [calendar components:NSYearCalendarUnit fromDate:today];
NSUInteger months = [calendar rangeOfUnit:NSMonthCalendarUnit
                                   inUnit:NSYearCalendarUnit
                                  forDate:today].length;
for (int i = 1; i <= months; i++) {
    components.month = i;
    NSDate *month = [calendar dateFromComponents:components];
    days += [calendar rangeOfUnit:NSDayCalendarUnit
                           inUnit:NSMonthCalendarUnit
                          forDate:month].length;
}

return days;

It is not as neat as I would have hoped for but it will work for any calendar such as the ordinary gregorian one or the islamic one.

Answer 2

In general you may use number of days between 1st day of the year and 1st day of the next year. Here's the code that illustrates this approach

- (NSDate *)firstDateOfYear:(NSInteger)year
{
    NSDateComponents *dc = [[NSDateComponents alloc] init];
    dc.year = year;
    dc.month = 1;
    dc.day = 1;
    return [[NSCalendar currentCalendar] dateFromComponents:dc];
}

- (NSUInteger)numberOfDaysInYear:(NSInteger)year
{
    NSDate *firstDateOfYear = [self firstDateOfYear:year];
    NSDate *firstDateOfNextYear = [self firstDateOfYear:year + 1];
    NSDateComponents *components = [[NSCalendar currentCalendar] components:NSDayCalendarUnit fromDate:firstDateOfYear toDate:firstDateOfNextYear options:0];
    return [components day];
}

Answer 3

I don't know objective-c but it is a simple algorithm to determine if it is a leap year.

if ( year % 400 == 0 )
   then 366 // Leap Year
else if ( year % 100 == 0 )
   then 365 // Non-Leap Year
else if ( year % 4 == 0 )
   then 366 // Leap Year
else
   365 // Non-Leap Year

Or if you want a little less verbose version

if ((year % 4 == 0) && (year % 100 != 0) || (year % 400 == 0))
   then 366 // Leap Year
else
   365 // Non-Leap Year

Answer 4

I don't know if anybody is still interested in this thread, but is another possible solution:

NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *startOfYear;
NSTimeInterval lengthOfYear;
[calendar rangeOfUnit:NSYearCalendarUnit
            startDate:&startOfYear
             interval:&lengthOfYear
              forDate:[NSDate date]];
NSDate *endOfYear = [startOfYear dateByAddingTimeInterval:lengthOfYear];
NSDateComponents *comp = [calendar components:NSDayCalendarUnit
                                     fromDate:startOfYear
                                       toDate:endOfYear
                                      options:0];
NSUInteger numberOfDaysInThisYear = [comp day];

using only 2 calls to NSCalendar.

Answer 5

Maybe you can use the components:fromDate:toDate:options: selector which is meant to (and I quote official Apple docs): Returns, as an NSDateComponents object using specified components, the difference between two supplied dates. ?

Also read this post that clarifies the behaviour you are seeing.