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;}