Xcode - Set week of month, then get the week of year - objective-c

Question

Currently trying to use NSDateFormatter and NSDateComponents to set the week number for a month, then find the week of year that would be.
Let’s say we have a date: 20/05/2020, then set the week number to 0, or 1, or 2, etc.. then find out the week of year from that.
So far with NSDateComponents I’ve tried doing:
NSDate *date = self.date; // 20/05/2020
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *components = [calendar components:NSCalendarUnitMonth | NSCalendarUnitYear fromDate:date];
[components setWeekOfMonth:1];
NSDate *newDate = [calendar dateFromComponents:components];
NSInteger weekOfYear = [calendar components:NSCalendarUnitWeekOfYear fromDate:newDate].weekOfYear;
I'm always getting the output 18.
Expected output:
Change week of month to: 1 | output: 19 (4th)
Change week of month to: 2 | output: 20 (11th)
Change week of month to: 3 | output: 21 (18th)
Change week of month to: 4 | output: 22 (25th)

Answer 1

The problem is setting setWeekOfMonth in the date components has no effect.
Instead set the weekday and weekdayOrdinal
NSDate *date = self.date; // 20/05/2020
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *components = [calendar components:NSCalendarUnitMonth | NSCalendarUnitYear fromDate:date];
components.weekday = 2;
components.weekdayOrdinal = 3;
NSDate *newDate = [calendar dateFromComponents:components];
NSInteger weekOfYear = [calendar components:NSCalendarUnitWeekOfYear fromDate:newDate].weekOfYear;
This is a different approach:
It calculates the first monday in the current month, then it enumerates the next mondays until the end of the month.
- (NSArray *)yearOfWeeksInCurrentMonth
{
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *components = [calendar components: NSCalendarUnitMonth | NSCalendarUnitYear fromDate:[NSDate date]];
components.weekday = 2;
components.weekdayOrdinal = 1;
NSDate *firstMonday = [calendar dateFromComponents:components];
NSInteger weekOfYear = [calendar component:NSCalendarUnitWeekOfYear fromDate:firstMonday];
__block NSMutableArray *result = [NSMutableArray array];
[result addObject:#[firstMonday, #(weekOfYear)]];
NSDateComponents *weekComponents = [calendar components: NSCalendarUnitWeekday fromDate:firstMonday];
[calendar enumerateDatesStartingAfterDate:firstMonday matchingComponents:weekComponents options:NSCalendarMatchNextTime usingBlock:^(NSDate * _Nullable date, BOOL exactMatch, BOOL * _Nonnull stop) {
if (date != nil) {
if ( [calendar component:NSCalendarUnitMonth fromDate:date] > components.month ) {
*stop = YES;
} else {
NSInteger weekOfYear = [calendar component:NSCalendarUnitWeekOfYear fromDate:date];
[result addObject:#[date, #(weekOfYear)]];
}
}
}];
return [result copy];
}
The return value is an array containing the date (NSDate) and the corresponding weekOfYear (NSNumber)
(
(
"2020-05-03 22:00:00 +0000",
19
),
(
"2020-05-10 22:00:00 +0000",
20
),
(
"2020-05-17 22:00:00 +0000",
21
),
(
"2020-05-24 22:00:00 +0000",
22
)
)