iOS获取某个日期后n个月的日期

-(NSDate *)getPriousorLaterDateFromDate:(NSDate *)date withMonth:(NSInteger)month
{
  NSDateComponents *comps = [[NSDateComponents alloc] init];
  [comps setMonth:month];
  NSCalendar *calender = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
  NSDate *mDate = [calender dateByAddingComponents:comps toDate:date options:0];
  return mDate;
}

- (NSDate *)getLaterDateFromDate:(NSDate *)date withYear:(NSInteger)year month:(NSInteger)month day:(NSInteger)day {
  NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
  NSDateComponents *comps = nil;
  comps = [calendar components:NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay fromDate:date];
  NSDateComponents *adcomps = [[NSDateComponents alloc] init];
  [adcomps setYear:year];
  [adcomps setMonth:month];
  [adcomps setDay:day];
  NSDate *newdate = [calendar dateByAddingComponents:adcomps toDate:date options:0];
  return newdate;
}