Getting first day of a week with NSDateComponents : changing year

Question

Hello I have a problem with setting a firstWeekDay, here is what I do:

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; 
comp = [gregorian components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSWeekCalendarUnit | NSWeekdayCalendarUnit) fromDate:targetDate];
[comp setWeekday:2];

NSDate *firstWeekDay = [gregorian dateFromComponents:comp];

If Saturday 2011-01-01 is targetDate, the firstWeekDay in my calendar appears to be Monday 2011-12-26, but in fact it should be Monday 2010-12-26. How can I make it right?

Is this possibly the reason why the alarm clock in iOS didn't work properly for some users on 2011-01-01? — Felix, Mar 18 '11 at 09:00

YvesJusot · Answer 1 · 2012-01-06T20:18:07.887

35

To fix this problem, Add NSYearForWeekOfYearCalendarUnit in the NSDateComponents.

Ex:

NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* comps = [calendar components:NSYearForWeekOfYearCalendarUnit |NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:curDate];

[comps setWeekday:2]; // 2: monday
firstDayOfTheWeek = [calendar dateFromComponents:comps];
[comps setWeekday:7]; // 7: saturday
lastDayOfTheWeek = [calendar dateFromComponents:comps];

edited Jan 06 '12 at 20:18

answered Jan 06 '12 at 20:11

YvesJusot

479
4
5

3

This was solution. If you still have some problem and used NSDayCalendarUnit then try to remove it. – Altynbek Usenbekov Jun 14 '13 at 04:03
Why do you need "NSYearForWeekOfYearCalendarUnit"? What does it do? – shim Nov 25 '13 at 14:19
1

@Raj, hehe, it actually made your "day" ;-)! – Mundi Mar 07 '15 at 17:23
Indeed, never realized! :D – Raj Pawan Gumdal Mar 07 '15 at 19:47

score 1 · Answer 2 · answered Jan 19 '14 at 19:03

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];
}

score 1 · Answer 3 · answered Nov 20 '14 at 16:43

The Swift solution (thanks @YvesJusot):

let calendar = NSCalendar.currentCalendar()
let comps = calendar.components(NSCalendarUnit.WeekOfYearCalendarUnit|NSCalendarUnit.YearCalendarUnit|NSCalendarUnit.MonthCalendarUnit|NSCalendarUnit.WeekCalendarUnit|NSCalendarUnit.WeekdayCalendarUnit, fromDate: NSDate()) as NSDateComponents

comps.setValue(2, forComponent: NSCalendarUnit.WeekdayCalendarUnit)
let monday = calendar.dateFromComponents(comps)!

println("\(monday)")

score 1 · Answer 4 · answered Oct 27 '15 at 14:20

You suppose to use dynamic values instead of hardcoding 2 as Monday!

NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* comps = [calendar components:NSYearForWeekOfYearCalendarUnit|NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:[NSDate date]];

comps.weekday = calendar.firstWeekday;
firstDayOfTheWeek = [calendar dateFromComponents:comps];
comps.weekday = calendar.firstWeekday - 1;
lastDayOfTheWeek = [calendar dateFromComponents:comps];

score 1 · Answer 5 · answered Mar 18 '11 at 08:40

1

Try this

// adjust them for first day of previous week (Monday)
[comp setWeekday:2];
[comp setWeek:([comp week] - 1)];

Note this solution assumes the first day of the week is Monday.

answered Mar 18 '11 at 08:40

Hanuman

642
5
19

Thank you, but your method is not working. firstWeekDay now became 2011-12-20 – Roman Mar 18 '11 at 09:17

score 0 · Answer 6 · answered Jul 31 '15 at 13:56

I did some changes in @JasonGarrett answer and it works for me.

let calendar = NSCalendar.currentCalendar()
let flags : NSCalendarUnit = NSCalendarUnit.CalendarUnitDay | NSCalendarUnit.CalendarUnitMonth | NSCalendarUnit.CalendarUnitYear
let comps = calendar.components(flags, fromDate: NSDate()) as NSDateComponents
                comps.setValue(2, forComponent: NSCalendarUnit.CalendarUnitWeekday)
let monday = calendar.dateFromComponents(comps)!

score 0 · Answer 7 · edited Dec 20 '17 at 10:01

// Make these two methods as categories to NSDate
// Use This to get First date of the week (Monday)

- (NSDate *) getFirstDayOfWeek {

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];

    NSDateComponents *compOfDate = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekday) fromDate:self];

    NSInteger numOfDaysToAdd = compOfDate.weekday == 1 ? -6 : (2 - compOfDate.weekday);

    NSDateComponents *compToAdd = [[NSDateComponents alloc] init];

    compToAdd.day = numOfDaysToAdd;

    return [calendar dateByAddingComponents:compToAdd toDate:self options:0];
}

// Use This to get last date of the week (Sunday)

- (NSDate *)getLastDayOfWeek {

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];

    NSDateComponents *compOfDate = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekday) fromDate:self];

    NSInteger numOfDaysToAdd = compOfDate.weekday == 1 ? 0 : (8 - compOfDate.weekday);

    NSDateComponents *compToAdd = [[NSDateComponents alloc] init];

    compToAdd.day = numOfDaysToAdd;

    return [calendar dateByAddingComponents:compToAdd toDate:self options:0];
}

Getting first day of a week with NSDateComponents : changing year

7 Answers7