NSCalendar first day of week

问题

Does anyone know if there is a way to set the first day of the week on a NSCalendar, or is there a calendar that already has Monday as the first day of the week, instead of Sunday. I'm currently working on an app that is based around a week's worth of work, and it needs to start on Monday, not Sunday. I can most likely do some work to work around this, but there will be a lot of corner cases. I'd prefer the platform do it for me.

Thanks in advance

Here's some the code that I'm using. it's saturday now, so what I would hope is that weekday would be 6, instead of 7. that would mean that Sunday would be 7 instead of rolling over to 0

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
[gregorian setFirstWeekday:0];
unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit |  NSDayCalendarUnit | NSWeekCalendarUnit | NSWeekdayCalendarUnit;
NSDateComponents *todaysDate = [gregorian components:unitFlags fromDate:[NSDate date]];
int dayOfWeek = todaysDate.weekday;

回答1:

Edit: This does not check the edge case where the beginning of the week starts in the prior month. Some updated code to cover this: https://stackoverflow.com/a/14688780/308315

In case anyone is still paying attention to this, you need to use

ordinalityOfUnit:inUnit:forDate:

and set firstWeekday to 2. (1 == Sunday and 7 == Saturday)

Here's the code:

NSCalendar *gregorian = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];
[gregorian setFirstWeekday:2]; // Sunday == 1, Saturday == 7
NSUInteger adjustedWeekdayOrdinal = [gregorian ordinalityOfUnit:NSWeekdayCalendarUnit inUnit:NSWeekCalendarUnit forDate:[NSDate date]];
NSLog(@"Adjusted weekday ordinal: %d", adjustedWeekdayOrdinal);

Remember, the ordinals for weekdays start at 1 for the first day of the week, not zero.

Documentation link.

回答2:

This code constructs a date that is set to Monday of the current week:

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

NSDate *today = [NSDate date];
NSDate *beginningOfWeek = nil;
BOOL ok = [gregorian rangeOfUnit:NSWeekCalendarUnit startDate:&beginningOfWeek
                                interval:NULL forDate: today];

回答3:

setFirstWeekday: on the NSCalendar object. Sets the index of the first weekday for the receiver.

- (void)setFirstWeekday:(NSUInteger)weekday

Should do the trick.

回答4:

In my opinion this settings should be dynamic according to the user locale. Therefore one should use:

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
[gregorian setLocale:[NSLocale currentLocale]];

This will cause the calendar to set the first week day according to the user locale automatically. Unless you are developing your app for a specific purpose/user locale (or prefer to allow the user to choose this day).

回答5:

I've done it like this.

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *today = [NSDate date];
NSDateComponents *compForWeekday = [gregorian components:(NSWeekdayCalendarUnit) fromDate:today];
NSInteger weekDayAsNumber = [compForWeekday weekday]; // The week day as number but with sunday starting as 1

weekDayAsNumber = ((weekDayAsNumber + 5) % 7) + 1; // Transforming so that monday = 1 and sunday = 7

回答6:

I had trouble with a lot of the answers here. . maybe it was just me. .

Here's an answer that works for me:

- (NSDate*)firstDayOfWeek
{
    NSCalendar* cal = [[NSCalendar currentCalendar] copy];
    [cal setFirstWeekday:2]; //Override locale to make week start on Monday
    NSDate* startOfTheWeek;
    NSTimeInterval interval;
    [cal rangeOfUnit:NSWeekCalendarUnit startDate:&startOfTheWeek interval:&interval forDate:self];
    return startOfTheWeek;
}

- (NSDate*)lastDayOfWeek
{
    NSCalendar* cal = [[NSCalendar currentCalendar] copy];
    [cal setFirstWeekday:2]; //Override locale to make week start on Monday
    NSDate* startOfTheWeek;
    NSTimeInterval interval;
    [cal rangeOfUnit:NSWeekCalendarUnit startDate:&startOfTheWeek interval:&interval forDate:self];
    return [startOfTheWeek dateByAddingTimeInterval:interval - 1];
}

Update:

As pointed out (elsewhere) by @vikingosegundo, in general its best to let the local determine which day is the start of the week, however in this case the OP was asking for the start of the week to occur on Monday, hence we copy the system calendar, and override the firstWeekDay.

回答7:

The problem with Kris' answer is the edge case where the beginning of the week starts in the prior month. Here's some easier code and it also checks the edge case:

// Finds the date for the first day of the week
- (NSDate *)getFirstDayOfTheWeekFromDate:(NSDate *)givenDate
{
    NSCalendar *calendar = [NSCalendar currentCalendar];

    // Edge case where beginning of week starts in the prior month
    NSDateComponents *edgeCase = [[NSDateComponents alloc] init];
    [edgeCase setMonth:2];
    [edgeCase setDay:1];
    [edgeCase setYear:2013];
    NSDate *edgeCaseDate = [calendar dateFromComponents:edgeCase];

    NSDateComponents *components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:edgeCaseDate];
    [components setWeekday:1]; // 1 == Sunday, 7 == Saturday
    [components setWeek:[components week]];

    NSLog(@"Edge case date is %@ and beginning of that week is %@", edgeCaseDate , [calendar dateFromComponents:components]);

    // Find Sunday for the given date
    components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:givenDate];
    [components setWeekday:1]; // 1 == Sunday, 7 == Saturday
    [components setWeek:[components week]];

    NSLog(@"Original date is %@ and beginning of week is %@", givenDate , [calendar dateFromComponents:components]);

    return [calendar dateFromComponents:components];
}

回答8:

I see misunderstanding in the other messages. The first weekday, whichever it is, has number 1 not 0. By default Sunday=1 as in the "Introduction to Date and Time Programming Guide for Cocoa: Calendrical Calculations":

"The weekday value for Sunday in the Gregorian calendar is 1"

For the Monday as a first workday the only remedy I have is brute force condition to fix the calculation

NSCalendar *cal=[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *comps = [cal components:NSWeekdayCalendarUnit fromDate:[NSDate date]];
// set to 7 if it's Sunday otherwise decrease weekday number
NSInteger weekday=[comps weekday]==1?7:[comps weekday]-1;

回答9:

Below also covers the edge case,

- (NSDate *)getFirstDayOfTheWeekFromDate:(NSDate *)givenDate
{
    NSCalendar *calendar = [NSCalendar currentCalendar];


   NSDateComponents *components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:givenDate];
    [components setWeekday:2]; // 1 == Sunday, 7 == Saturday
    if([[calendar dateFromComponents:components] compare: curDate] == NSOrderedDescending) // if start is later in time than end
    {
        [components setWeek:[components week]-1];
    }

    return [calendar dateFromComponents:components];
}

回答10:

Try this:

NSCalendar *yourCal = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]
[yourCal setFirstWeekday:0];

回答11:

Iv found out the way to display any weekday name using nscalender..using the following code.. Just open your console from xcode menu bar to see the results.Copy Paste the following code in your viewDidLoad method to get the first day of the week

NSDate *today = [NSDate date];
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"MM/dd/yyyy :EEEE"];
NSString *dateString = [dateFormat stringFromDate:today];
NSLog(@"date: %@", dateString);
[dateFormat release];
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

NSDateComponents *components = [gregorian components:NSWeekdayCalendarUnit | NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:today];
[components setDay:([components day]-([components weekday]-1))];

NSDate *beginningOfWeek = [gregorian dateFromComponents:components];
NSDateFormatter *dateFormat_first = [[NSDateFormatter alloc] init];
[dateFormat_first setDateFormat:@"MM/dd/yyyy :EEEE"];
NSString *dateString_first = [dateFormat_first stringFromDate:beginningOfWeek];
NSLog(@"First_date: %@", dateString_first);

The Output will be:

 date: 02/11/2010 :Thursday
 First_date: 02/07/2010 :Sunday

since i had run this program on 2/11/2010 u will get the desired output depending on the current date.

Similarly if u want to get the first working day of the week i.e Monday's date then just modify the code a bit:

CHANGE :[components setDay:([components day]-([components weekday]-1))];

TO [components setDay:([components day]-([components weekday]-2))];

to get Mondays date for that week..

Similarly u can try to find the date of any of seven workdays by changing the integer -1,-2 and so on...

Hope u r question is answered..

Thanks, Bonson Dias

回答12:

My simple way of doing this is to get Monday = 0, Sunday = 6:

    NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:NSWeekdayCalendarUnit fromDate:[NSDate date]];
    NSInteger dayNumStartingFromMonday = ([dateComponents weekday] - 2 + 7) % 7;    //normal: Sunday is 1, Monday is 2

回答13:

The ISO 8601 calendar appears to have it's first weekday set to monday by default.

回答14:

Using the Calendar nextWeekend (iOS 10 or later) and ordinality (thanks @kris-markel). I've gotten Monday as first of the week for the en_US calendar.

Here is an example of it with fallback to firstWeekday:

extension Calendar {
    var firstWorkWeekday: Int {
        guard #available(iOS 10.0, *) else{
            return self.firstWeekday
        }
        guard let endOfWeekend = self.nextWeekend(startingAfter: Date())?.end else {
            return self.firstWeekday
        }
        return self.ordinality(of: .weekday, in: .weekOfYear, for: endOfWeekend) ?? self.firstWeekday
    }
}

回答15:

You can just change .firstWeekday of the calendar.

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
calendar.firstWeekday = 2;

Then use rangeOfUnit:startDate:interval:forDate: to get the first day

NSDate *startOfWeek;
[calendar rangeOfUnit:NSCalendarUnitWeekOfYear startDate:&startOfWeek interval:nil forDate:[NSdate date]];

回答16:

The Swift solution (note, use .yearForWeekOfYear, not .year):

let now = Date()
let cal = Calendar.current
var weekComponents = cal.dateComponents([.yearForWeekOfYear, .weekOfYear,
                                         .weekday], from: now)
//weekComponents.weekday = 1  // if your week starts on Sunday
weekComponents.weekday = 2  // if your week starts on Monday
cal.date(from: weekComponents) // returns date with first day of the week