//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;

 }