Question

I'm adding repeating events to a Cocoa app I'm working on. I have repeat every day and week fine because I can define these mathematically (3600*24*7 = 1 week). I use the following code to modify the date:

[NSDate dateWithTimeIntervalSinceNow:(3600*24*7*(weeks))]

I know how many months have passed since the event was repeated but I can't figure out how to make an NSDate object that represents 1 month/3 months/6 months/9 months into the future. Ideally I want the user to say repeat monthly starting Oct. 14 and it will repeat the 14th of every month.

Was it helpful?

Solution

(Almost the same as this question.)

From the documentation:

Use of NSCalendarDate strongly discouraged. It is not deprecated yet, however it may be in the next major OS release after Mac OS X v10.5. For calendrical calculations, you should use suitable combinations of NSCalendar, NSDate, and NSDateComponents, as described in Calendars in Dates and Times Programming Topics for Cocoa.

Following that advice:

NSDate *today = [NSDate date];

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

NSDateComponents *components = [[NSDateComponents alloc] init];
components.month = 1;
NSDate *nextMonth = [gregorian dateByAddingComponents:components toDate:today options:0];
[components release];

NSDateComponents *nextMonthComponents = [gregorian components:NSYearCalendarUnit | NSMonthCalendarUnit fromDate:nextMonth];

NSDateComponents *todayDayComponents = [gregorian components:NSDayCalendarUnit fromDate:today];

nextMonthComponents.day = todayDayComponents.day;
NSDate *nextMonthDay = [gregorian dateFromComponents:nextMonthComponents];

[gregorian release];

There may be a more direct or efficient implementation, but this should be accurate and should point in the right direction.

OTHER TIPS

Use NSCalender, NSDateComponents and NSDate:

NSDateComponents *components = [[[NSDateComponents alloc] init] autorelease];
components.month = 1;
NSDate *oneMonthFromNow = [[NSCalendar currentCalendar] dateByAddingComponents:components toDate:[NSDate date] options:0];

Just set the different properties of components to get different periods of time (e.g. 3 months, 6 months etc).

Note: Depending on the context, you may want to use [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease] instead of [NSCalendar currentCalendar], if by "1 month" you mean "1 month on the Gregorian calendar".

I'll probably use NSCalendarDate.

Get current date's dayOfMonth, monthOfYear and yearOfCommonEra, as three numbers.

Add the required number of months (1/3/6/9), taking care of 1) whether that date exist (e.g. 31 April, 29 Feb on a non-leap year), and 2) roll-over of year.

Create that new date with NSCalendarDate's initWithYear:month:day:hour:minute:second:timeZone:

NSCalendarDate is no longer supported by new SDK , will have problem while building for distribution.

You can do like the below:

NSDate *today = [NSDate date];

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

NSDateComponents *components = [[NSDateComponents alloc] init];
components.month = 1;
NSDate *nextMonth = [gregorian dateByAddingComponents:components toDate:today options:0];
[components release];

NSDateComponents *nextMonthComponents = [gregorian components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:nextMonth];
NSDate *nextMonthDay = [gregorian dateFromComponents:nextMonthComponents];

[gregorian release]; 
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