Get an array of future NSDates

Question

I have a date picker.

After choosing a time from this I would like to get the dates of the next 64 Mondays.

How would I go about writing a method to take a date and return an NSArray of NSDates for the next 64 Mondays from that date

for e.g. I picked time 6:45 pm from date picker then I want to fetch next 64 mondays with there time set to that time.

Answer 1

Example (ARC):

NSDate *pickerDate = [NSDate date];
NSLog(@"pickerDate: %@", pickerDate);

NSDateComponents *dateComponents;
NSCalendar *calendar = [NSCalendar currentCalendar];

dateComponents = [calendar components:NSWeekdayCalendarUnit fromDate:pickerDate];
NSInteger firstMondayOrdinal = 9 - [dateComponents weekday];
dateComponents = [[NSDateComponents alloc] init];
[dateComponents setDay:firstMondayOrdinal];
NSDate *firstMondayDate = [calendar dateByAddingComponents:dateComponents toDate:pickerDate options:0];

dateComponents = [[NSDateComponents alloc] init];
[dateComponents setWeek:1];

for (int i=0; i<64; i++) {
    [dateComponents setWeek:i];
    NSDate *mondayDate = [calendar dateByAddingComponents:dateComponents toDate:firstMondayDate options:0];
    NSLog(@"week#: %i, mondayDate: %@", i, mondayDate);
}

NSLog output:
pickerDate: 2011-12-09 20:38:25 +0000
week#: 0, mondayDate: 2011-12-12 20:38:25 +0000
week#: 1, mondayDate: 2011-12-19 20:38:25 +0000
week#: 2, mondayDate: 2011-12-26 20:38:25 +0000
week#: 3, mondayDate: 2012-01-02 20:38:25 +0000
-the remaining 60 here-

Answer 2

Start with the NSDate from the picker, and keep adding 24*60*60 seconds to it until it's a Monday. Add the resulting date to the result. Continue adding 7*24*60*60 seconds to the last date you added and pushing the result onto the return list until you have all 64 Mondays. Here is how you tell if a NSDate falls on Monday:

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *weekdayComponents =[gregorian components:NSWeekdayCalendarUnit fromDate:dateOfInterest];
NSInteger weekday = [weekdayComponents weekday];
if (weekday == 2) ... // 2 represents Monday

EDIT: DaveDeLong pointed out a deficiency in the above algorithm: it will shift the time two times on the days of changing to daylight savings time. Instead of counting seconds manually, use this code to add a day to NSDate:

NSDate *currentDate = [NSDate date];
NSDateComponents *comps = [[NSDateComponents alloc] init];
[comps setDay:1]; // Add 1 when searching for the next Monday; add 7 when iterating 63 times 
NSDate *date = [gregorian dateByAddingComponents:comps toDate:currentDate  options:0];
[comps release];

Answer 3

You can use NSCalendar to determine what day of the week today (at the chosen time) is; bump it up to get to the next Monday, and then bump that by by 7 days 63 times to get the Mondays you seem to want.