Get the Week Number in iOS SDK - objective-c

Question

I want to get the Week number of the year from the date.I tried the code as follow but gives me a wrong week number.
My code for week number:
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"YYYY-MM-dd"];
NSDate *date = [dateFormatter dateFromString:#"2012-09-15"];
NSCalendar *calendar = [NSCalendar currentCalendar];
NSLog(#"week: %i", [[calendar components: NSWeekOfYearCalendarUnit fromDate:date] weekOfYear]); //Display 38 instead of 37
}
Note: If i try with with [NSDate date] display the correct.
Help me to solve this..
Thank you,

Answer 1

ObjectiveC:
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *dateComponent = [calendar components:(NSWeekOfYearCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit) fromDate:[NSDate date]];
NSLog(#"%#",dateComponent);
Update
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *dateComponent = [calendar components:(NSCalendarUnitWeekOfYear | NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear) fromDate:date];
NSLog(#"%#",dateComponent);
Swift:
let calendar = NSCalendar.currentCalendar()
let dateComponent = calendar.components([.WeekOfYear, .Day, .Month, .Year], fromDate: NSDate(timeIntervalSinceNow: 0))
print("weekOfYear \(dateComponent.weekOfYear)")
Swift 3 - Swift 5:
let component = Calendar.current.component(.weekOfYear, from: Date())
print("Week of Year \(component)")

Answer 2

[NSCalendar currentCalendar] gives you a Gregorian Calendar as default. You can use
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSISO8601Calendar];
to get an ISO 08601 conform calendar, which has week number 37 for your date.

Answer 3

Swift 3:
You need know last Date of selected month. Than check number of week for this week, and this will be your number of weeks in month
return Calendar.current.component(.weekOfMonth, from: lastDate ?? Date())

Answer 4

Updated code in ObjectiveC used Xcode version - 9.1 - :
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *dateComponent = [calendar components:(NSCalendarUnitWeekOfYear | NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear) fromDate:[NSDate date]];
NSLog(#"%ld",(long)[dateComponent weekOfYear]);