Objective-C: find date given day of the year and year - objective-c

Question

I'm writing a GUI for a legacy data object where a date is saved in the integer properties day of the year and year (real "genius" design...)
How can I convert this data into day and month given the year?
I'm currently trying:
int theYear = 2016;
int theDayOfTheYear = 222;
NSCalendar* gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *components = [[NSDateComponents alloc] init];
[components setYear:theYear];
[components setDay:theDayOfTheYear];
NSDate* theDate = [gregorian dateFromComponents:components];
This seems a bit too hacky to me. It could be just coincidence that it works with days >31 - haven't found any mention of this in the NSDateComponents class reference.
When I debug, po theDate gives me 2016-08-08 22:00:00 +0000
--> close, but it should be 2016-08-09 (!)
To perform the reverse operation, i.e. to convert a normal DD-MM-YYYY date into day of the year, I'm using this code:
NSDate *fullDate = [NSDate date];
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSUInteger dayOfYear = [gregorian ordinalityOfUnit:NSDayCalendarUnit
inUnit:NSYearCalendarUnit
forDate:fullDate];
But I can't seem to find the proper methods to do the opposite...

Answer 1

Sometimes a test is all takes :)
Don't forget that NSDate are GMT, so you might want to add [[NSTimeZone localTimeZone] secondsFromGMT] seconds to it.
It seems that you have it working :)
- (void) testDate
{
int startYear = 2016;
int startMonth = 1;
int startDay = 1;
// Create the startDate
NSDateComponents * startDateComp = [NSDateComponents new];
startDateComp.day = startDay;
startDateComp.month = startMonth;
startDateComp.year = startYear;
NSDate * startDate = [[NSCalendar currentCalendar] dateFromComponents:startDateComp];
for(int i=0 ; i < 365; i++)
{
// add i day to startDate
NSDate * testDate = [startDate dateByAddingTimeInterval:i * 24 * 60 * 60];
NSUInteger dayOfYear = [[NSCalendar currentCalendar] ordinalityOfUnit:NSDayCalendarUnit
inUnit:NSYearCalendarUnit
forDate:testDate];
XCTAssert(dayOfYear == (i + 1), #"the day of the year should be i + 1");
// Create a date using day of year
NSDateComponents *components = [[NSDateComponents alloc] init];
[components setYear:startYear];
[components setDay:dayOfYear];
NSDate* resultDate = [[NSCalendar currentCalendar] dateFromComponents:components];
// testing result date against test date
NSInteger test, result;
test = [[NSCalendar currentCalendar] component:NSCalendarUnitDay fromDate:testDate];
result = [[NSCalendar currentCalendar] component:NSCalendarUnitDay fromDate:resultDate];
XCTAssert(test == result);
test = [[NSCalendar currentCalendar] component:NSCalendarUnitMonth fromDate:testDate];
result = [[NSCalendar currentCalendar] component:NSCalendarUnitMonth fromDate:resultDate];
XCTAssert(test == result);
test = [[NSCalendar currentCalendar] component:NSCalendarUnitYear fromDate:testDate];
result = [[NSCalendar currentCalendar] component:NSCalendarUnitYear fromDate:resultDate];
XCTAssert(test == result);
}

Answer 2

Please try this. Its the larger calendar unit NSCalendarUnitEra :)
NSDate *fullDate = [NSDate date];
NSCalendar *gregorian = [NSCalendar currentCalendar];
gregorian.timeZone = [NSTimeZone systemTimeZone];
NSUInteger dayOfYear = [gregorian ordinalityOfUnit:NSCalendarUnitDay
inUnit:NSCalendarUnitEra
forDate:fullDate];
NSDateComponents *dateCom = [[NSDateComponents alloc] init];
dateCom.day = dayOfYear;
NSDate *expectedDate = [gregorian dateFromComponents:dateCom];
NSLog(#"%#",expectedDate);