Comparing NSDate + Period

Question

I have start date and a duration (period). For example startDate = '2014-02-12' period = 2. I desired dates 2014-02-12, 2014-02-14, 2014-02-16, .... I need to determine the current date is flagged during.

Answer 1

To check if the difference between the start date and the current date is an even number of days, use NSDateComponents:

NSDate *startDate = ...;
NSDate *currentDate = [NSDate date];
NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *diff = [cal components:NSDayCalendarUnit fromDate:startDate
                                  toDate:currentDate options:0];
NSInteger days = diff.day;
if (days % 2 == 0) {
    // even number of days between start date and current date
}

Answer 2

You can get the desired dates using

- (id)dateByAddingTimeInterval:(NSTimeInterval)seconds

with seconds = period*3600*24

Answer 3

Calc the days from startDate to givenData, check the result whether it can be divisible by the period.

+ (NSInteger)daysWithinEraFromDate:(NSDate *)startDate toDate:(NSDate *)endDate {
    NSCalendar *gregorian = [[NSCalendar alloc]
                             initWithCalendarIdentifier:NSGregorianCalendar];
    [gregorian setTimeZone:[NSTimeZone localTimeZone]];
    // for timezone issue
    NSDate *newDate1 = [startDate dateByAddingTimeInterval:[[NSTimeZone localTimeZone] secondsFromGMT]];
    NSDate *newDate2 = [endDate dateByAddingTimeInterval:[[NSTimeZone localTimeZone] secondsFromGMT]];
    NSInteger startDay = [gregorian ordinalityOfUnit:NSDayCalendarUnit
                                            inUnit: NSEraCalendarUnit forDate:newDate1];
    NSInteger endDay = [gregorian ordinalityOfUnit:NSDayCalendarUnit
                                          inUnit: NSEraCalendarUnit forDate:newDate2];
    return endDay - startDay;
}