Xcode如何计算两个日期之间的月份数

-(int)differenceInMonthsFrom:(NSDate*)older to:(NSDate*)younger {
  NSCalendar *calendar=[NSCalendar currentCalendar];
  NSDateComponents *components=[calendar components:NSMonthCalendarUnit fromDate:older toDate:younger options:0];
  return [components month];
}

NSDate

 NSDate *now=[NSDate date];   // this is **now** date object
 NSDate *lastSaved=[NSdate lastDate];   // this is last saved object
 NSComparisonResult duration=[now timeIntervalSinceDate:lastSaved];   //this will return time interval between this 2 date object in seconds
 hoursInterval=duration/3600;  // this will return hours of interval between this 2 date
 daysInterval=hoursInterval/24;  // this will return days interval between this 2 date
 monthsInterval=daysInterval/30;  // and this will return month interval between this 2 date