iOS and Objective-C: Repeating an event every quarter

Question

I need to have an event repeat every "quarter" (which I assume means moving up 3 months approximately). So I could expect this to move the date (but it doesn't):

    NSDateComponents *component = [[NSDateComponents alloc] init]; // quarter
    component.quarter = 1;

    self.todoStartDate = [[NSCalendar currentCalendar] dateByAddingComponents: component toDate:self.todoStartDate options: 0];

Is there anything wrong with adding a "quarter" to a date? It works fine when adding a day or a week, but not with a "quarter".

Perhaps alternatively you could simply use the first day of four different months, e.g. January, April, July, and October (depends on whether you are specifically using Gregorian calendar etc) — dreamlax, Jul 28 '12 at 09:09
Thanks. That's the thing: I don't want to make the assumption for which calendar the user is setup with. I'd rather let the foundation class handle this calculation. But it doesn't seem to do this, and I can't find any more documentation on it. — Z S, Jul 28 '12 at 09:17

score 0 · Answer 1 · edited May 23 '17 at 12:12

(I wish I could add this as a formatted comment on applefreak's answer, which is a pretty good one. But SO doesn't allow markup in comments.)

Apple's documentation for NSCalendar says:

Some calendars represented by this API may have to map their basic unit concepts into year/month/week/day/… nomenclature. For example, a calendar composed of 4 quarters in a year instead of 12 months uses the month unit to represent quarters.

Now, this could be a lot clearer, but I think what Apple is saying is that normal calendars don't have "quarters" at all; they only have years, months (12 of them), and days. But you can subclass NSCalendar (or create a new instance of NSCalendar?) so that the year has only 4 months, and then call those months "quarters", and for the benefit of such subclasses Apple has pre-defined the quarter property. This is horribly confusing; I bet there's a good story behind Apple's WTFery here.

Anyway, I agree with applefreak that you should be dealing in year/month/day dates anyway, not mucking around with mythical "quarters." After all, what would it even mean to "add", let's say, two quarters to March 31, given that Q3 is shorter than Q1? (And would the answer depend on whether this was a leap year?)

If what you really want is "an event recurring every year on January 1, April 1, July 1, and October 1," then you should write that. Don't even bother with "adding three months", which has the same problems as "adding one quarter".

BTW, other people here have noticed the quarter WTF as well. For example: I want to get a quarter value in NSDateComponents class

score 0 · Answer 2 · answered Jun 18 '13 at 09:38

I faced the same issue, don't know why the quarter doesn't work, so workaround by replacing quarter by month * 3. The following demonstrates how to get three quarters backward:

        NSDateComponents *dayComponent = [[NSDateComponents alloc] init];
        NSCalendar *theCalendar = [NSCalendar currentCalendar];

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        dateFormatter.dateFormat = @"QQQ yyyy";
        NSDate *currentDate = [NSDate date];

        for (int i = -2; i <= 0; i++) {
            //dayComponent.quarter = i;
            dayComponent.month = i*3;

            NSDate *date = [theCalendar dateByAddingComponents:dayComponent toDate:currentDate options:0];

            NSString *dateString = [dateFormatter stringFromDate:date];

            NSLog(@"date = %@", dateString);
        }

I hope all this helps.

iOS and Objective-C: Repeating an event every quarter

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