- (BOOL)isEqualToDate:(NSDate *)otherDate;

    與otherDate比較，相同返回YES


    - (NSDate *)earlierDate:(NSDate *)anotherDate;

    與anotherDate比較，返回較早的那個日期


    - (NSDate *)laterDate:(NSDate *)anotherDate;

    與anotherDate比較，返回較晚的那個日期



    - (NSComparisonResult)compare:(NSDate *)other;

    該方法用于排序時調用:

      . 當實例保存的日期值與anotherDate相同時返回NSOrderedSame

      . 當實例保存的日期值晚于anotherDate時返回NSOrderedDescending

      . 當實例保存的日期值早于anotherDate時返回NSOrderedAscending

 // 獲得本地時間指定時區(qū)
                    NSDate *dates = [NSDate date];
                    NSDateFormatter *formatter =  [[NSDateFormatter alloc] init];
                    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
                    NSTimeZone* timeZone = [NSTimeZone timeZoneWithName:@"Asia/beijing"];
                    [formatter setTimeZone:timeZone];
                    NSString *loctime = [formatter stringFromDate:dates];

(NSDate *) stringToDate:string
{
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    NSDate *date = [dateFormatter dateFromString:string];
    [dateFormatter release];
    return date;
}

-(NSInteger)daysWithinEraFromDate:(NSDate *) startDate toDate:(NSDate *) endDate
{
    NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    unsigned int unitFlags = NSDayCalendarUnit;
    NSDateComponents *comps = [gregorian components:unitFlags fromDate:startDate  toDate:endDate  options:0];
    int days = [comps day];
    return days;
}