24 hours divided by 30 minutes apart - NSDate - objective-c

Question

I'm trying to get an NSMutableArray of NSDates each NSDate object targets the nearest rounded either HH:00 or HH:30 for the next 24 hours from now.
lets say right now its 02:31 I want an output of #[03:00,03:30,04:00,04:30...03:00(of the next day)]
if its 02:29 then I want #[02:30,03:00 and so on till the next day at 02:30].
right now I have the code below and it works almost all the time, yet rarely I get an output of all the NSDate objects that I want with a remainder of an extra minute(#[03:01,03:31:04:01...so on]).
any ideas ?
-(NSMutableArray*)TwentyFourHoursFromNowDivicedBy30Mins
{
NSMutableArray * dateArray = [NSMutableArray array];
NSCalendar * cal = [NSCalendar currentCalendar];
NSDateComponents * plusDays = [NSDateComponents new];
NSDate * now = [self changeTimeValue:[NSDate date]];
for( NSUInteger day = 0; day < 2; day++ )
{
[plusDays setDay:day];
[dateArray addObject:[cal dateByAddingComponents:plusDays toDate:now options:0]];
}
NSDate *startDate = [dateArray objectAtIndex:0];
NSDate *endDate = [dateArray objectAtIndex:1];
NSDateComponents *diff = [[NSDateComponents alloc] init];
[diff setMinute:0];
NSCalendar *calz = [NSCalendar currentCalendar];
NSDate *tmp = startDate;
NSMutableArray *dates = [NSMutableArray arrayWithObject:tmp];
while ([tmp laterDate:endDate] == endDate) {
[diff setMinute:[diff minute] + 30];
tmp = [calz dateByAddingComponents:diff toDate:startDate options:0];
[dates addObject:tmp];
}
return dates;
}
- (NSDate *)changeTimeValue:(NSDate *)dateValue{
NSDateComponents *time = [[NSCalendar currentCalendar]
components:NSHourCalendarUnit | NSMinuteCalendarUnit
fromDate:dateValue];
long val = 0;
NSDate *newDate = [[NSDate alloc] init];
NSInteger minutes = [time minute];
if(minutes > 0 && minutes < 30) {
val = 30 - minutes; NSTimeInterval aTimeInterval = [dateValue
timeIntervalSinceReferenceDate] + 60 * val + minutes;
newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
return newDate;
} else if(minutes > 30 && minutes < 60) {
val = 60 - minutes;
NSTimeInterval aTimeInterval = [dateValue timeIntervalSinceReferenceDate]
+ 60 * val;
newDate = [NSDate dateWithTimeIntervalSinceReferenceDate:aTimeInterval];
return newDate;
} else {
return newDate;
}
}

Answer 1

You're not zeroing out the seconds in your changeTimeValue, and in any case I think you've overcomplicated it. So I suspect you're subsequently seeing rounding issues. Just use NSDateComponents to do the whole job:
NSCalendar *currentCalendar = [NSCalendar currentCalendar];
NSDateComponents *dateComponents = [currentCalendar
components:NSHourCalendarUnit |
NSMinuteCalendarUnit |
NSYearCalendarUnit |
NSMonthCalendarUnit |
NSDayCalendarUnit
fromDate:dateValue];
dateComponents.minute += 15;
dateComponents.minute -= dateComponents.minute%30;
return [currentCalendar dateFromComponents:dateComponents];