Convert week number for a certain year to a month name - ios

Question

After searching through SO but apart from this question I found no solutions. I'm thinking about creating a method that would accept the int of the week number and the int of the year and that would return an NSString with the name of the month:
- (NSString *)getMonthNameFromNumber:(int)weekNumber andYear:(int)year
But I can't find a way to approach this problem. Would be glad if anyone could help with advices.

Answer 1

Something like this will do
- (NSString *)monthNameForWeek:(NSUInteger)week inYear:(NSInteger)year {
NSDateComponents * dateComponents = [NSDateComponents new];
dateComponents.year = year;
dateComponents.weekOfYear = week;
dateComponents.weekday = 1; // 1 indicates the first day of the week, which depends on the calendar
NSDate * date = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:#"MMMM"];
return [formatter stringFromDate:date];
}
Note that this is dependent on the current calendar set in the device preferences.
In case this doesn't fit your needs, you can provide a NSCalendar instance and use it to retrieve the date instead of using currentCalendar. By doing so you can configure things like which is the first day of the week and so on. The documentation of NSCalendar is worth a read.
If using a custom calendar is a common case, just change the implementation to something like
- (NSString *)monthNameForWeek:(NSUInteger)week inYear:(NSInteger)year {
[self monthNameForWeek:week inYear:year calendar:[NSCalendar currentCalendar]];
}
- (NSString *)monthNameForWeek:(NSUInteger)week inYear:(NSInteger)year calendar:(NSCalendar *)calendar {
NSDateComponents * dateComponents = [NSDateComponents new];
dateComponents.year = year;
dateComponents.weekOfYear = week;
dateComponents.weekday = 1; // 1 indicates the first day of the week, which depends on the calendar
NSDate * date = [calendar dateFromComponents:dateComponents];
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:#"MMMM"];
return [formatter stringFromDate:date];
}
As an unrelated side note, you should avoid get for methods names, unless you are returning a value indirectly.

Answer 2

With anything to do with dates, you need to involve a calendar. Your question assumes the Gregorian Calendar, but I suggest you change your method declaration to:
- (NSString*)monthNameFromWeek:(NSInteger)week year:(NSInteger)year calendar:(NSCalendar*)cal;
From this, there is also the ambiguity of which day we're talking about. For example (this hasn't been checked), week 4 of 2015 may contain both January and February. Which one is correct? For this example, we'll use a weekday of 1, which indicates Sunday (in the UK Gregorian Calendar), and we'll use whatever month this falls in to.
As such, your code would be:
// Set up our date components
NSDateComponents* comp = [[NSDateComponents alloc] init];
comp.year = year;
comp.weekOfYear = week;
comp.weekday = 1;
// Construct a date from components made, using the calendar
NSDate* date = [cal dateFromComponents:comp];
// Create the month string
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"MMMM"];
return [dateFormatter stringFromDate:date];