ios – 两个日期之间特定日期过了多少次？

我想要做的是获取两个日期之间每月特定日期的次数.

例如：
我想要在2011年11月21日至2013年5月15日期间每月16日过多少次.
在这种情况下,它将是17.

我一直在努力解决这个问题.我知道如何解决这个问题的唯一方法是编写一堆if语句来检查已经过了多少年,然后已经过了多少个月等等.有没有更快的方法,比如使用NSDate或其他什么？

解决方法

好的,这是一个 gist的工作示例.代码的内容是：

const NSCalendarUnit units = NSEraCalendarUnit|NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSCalendarCalendarUnit|NSTimeZoneCalendarUnit;
NSDateComponents *comps = [calendar components:units
                                      fromDate:startDate];
if ([comps day] > wantDay)
    nextMonth(comps);       // Missed the first month
[comps setDay:wantDay];

NSInteger count = 0;
while (YES) {
    NSDate *compareDate = [calendar dateFromComponents:comps];
    if (!compareDate) {
        NSLog(@"Failed to create compare date");
        return 5;
    }
    NSLog(@"Comparing %@",[formatter stringFromDate:compareDate]);
    if ([compareDate compare:endDate] == NSOrderedDescending)
        break;
    count++;
    nextMonth(comps);
}

nextMonth()的位置是：

static void nextMonth(NSDateComponents *comps) {
    NSInteger month = [comps month];
    if (month == 12) {
        [comps setYear:[comps year] + 1];
        [comps setMonth:1];
    } else {
        [comps setMonth:month + 1];
    }
}

示例输出：

$./dateiter 19990112 19990212 12
2014-01-16 13:06:53.189 dateiter[16740:707] start-date=1999-01-12 00:00:00 +0000,end-date=1999-02-12 00:00:00 +0000,want-day=12
2014-01-16 13:06:53.189 dateiter[16740:707] Comparing 19990112
2014-01-16 13:06:53.190 dateiter[16740:707] Comparing 19990212
2014-01-16 13:06:53.190 dateiter[16740:707] Comparing 19990312
2014-01-16 13:06:53.190 dateiter[16740:707] 2 months

$./dateiter 20111121 20130515 16
2014-01-16 13:10:53.318 dateiter[16810:707] start-date=2011-11-21 00:00:00 +0000,end-date=2013-05-15 00:00:00 +0000,want-day=16
2014-01-16 13:10:53.319 dateiter[16810:707] Comparing 20111216
2014-01-16 13:10:53.319 dateiter[16810:707] Comparing 20120116
2014-01-16 13:10:53.319 dateiter[16810:707] Comparing 20120216
2014-01-16 13:10:53.319 dateiter[16810:707] Comparing 20120316
2014-01-16 13:10:53.320 dateiter[16810:707] Comparing 20120416
2014-01-16 13:10:53.320 dateiter[16810:707] Comparing 20120516
2014-01-16 13:10:53.320 dateiter[16810:707] Comparing 20120616
2014-01-16 13:10:53.320 dateiter[16810:707] Comparing 20120716
2014-01-16 13:10:53.321 dateiter[16810:707] Comparing 20120816
2014-01-16 13:10:53.321 dateiter[16810:707] Comparing 20120916
2014-01-16 13:10:53.321 dateiter[16810:707] Comparing 20121016
2014-01-16 13:10:53.322 dateiter[16810:707] Comparing 20121116
2014-01-16 13:10:53.322 dateiter[16810:707] Comparing 20121216
2014-01-16 13:10:53.322 dateiter[16810:707] Comparing 20130116
2014-01-16 13:10:53.322 dateiter[16810:707] Comparing 20130216
2014-01-16 13:10:53.323 dateiter[16810:707] Comparing 20130316
2014-01-16 13:10:53.323 dateiter[16810:707] Comparing 20130416
2014-01-16 13:10:53.323 dateiter[16810:707] Comparing 20130516
2014-01-16 13:10:53.323 dateiter[16810:707] 17 months