iOS 计算两个日期之间的天数问题

 //获取当前时间若干年、月、日之后的时间
 + (NSDate *)dateWithFromDate:(NSDate *)date years:(NSInteger)years months:(NSInteger)months days:(NSInteger)days{
     NSDate  * latterDate;
     if (date) {
         latterDate = date;
     }else{
         latterDate = [NSDate date];
     }
     NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
     NSDateComponents *comps = [calendar components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay|NSCalendarUnitHour|NSCalendarUnitMinute
                                           fromDate:latterDate];
 
     [comps setYear:years];
     [comps setMonth:months];
     [comps setDay:days];
 
     return [calendar dateByAddingComponents:comps toDate:latterDate options:];
 }

 /**
  * @method
  *
  * @brief 获取两个日期之间的天数
  * @param fromDate       起始日期
  * @param toDate         终止日期
  * @return    总天数
  */
 + (NSInteger)numberOfDaysWithFromDate:(NSDate *)fromDate toDate:(NSDate *)toDate{
     NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
 
     NSDateComponents    * comp = [calendar components:NSCalendarUnitDay
                                              fromDate:fromDate
                                                toDate:toDate
                                               options:NSCalendarWrapComponents];
     NSLog(@" -- >>  comp : %@  << --",comp);
     return comp.day;
 }

根据以上两个方法可以获得更多根据日期计算天数的方法，只是在获取日期时传的参数不同，在此就不一一列举了。