+(NSInteger)getDaysFrom:(NSDate *)serverDate To:(NSDate *)endDate

{

    NSCalendar *gregorian = [[NSCalendar alloc]

                             initWithCalendarIdentifier:NSCalendarIdentifierGregorian];

    [gregorian setFirstWeekday:2];

    //去掉时分秒信息

    NSDate *fromDate;

    NSDate *toDate;

    [gregorian rangeOfUnit:NSCalendarUnitDay startDate:&fromDate interval:NULL forDate:serverDate];

    [gregorian rangeOfUnit:NSCalendarUnitDay startDate:&toDate interval:NULL forDate:endDate];

    NSDateComponents *dayComponents = [gregorian components:NSCalendarUnitDay fromDate:fromDate toDate:toDate options:0];

    return dayComponents.day;

}

//比较选择的开始时间和结束时间的大小

+(BOOL)ComparisonString:(NSString *)str1 andString:(NSString *)str2

{

    // NSString *dateStr=@"2015-12-31 01:01:01";//传入时间

    //1.获得时间

    NSDate *senddate = [ NSDate date ];

    NSDateFormatter *dateformatter = [[ NSDateFormatter alloc ] init];

    [dateformatter setDateFormat : @"yyyy-MM-dd" ];

    NSString *locationString = [dateformatter stringFromDate :senddate];

    str2 = locationString;

    NSArray *arrya1 = [str1 componentsSeparatedByString:@" " ];

    str1 = arrya1.firstObject;

    arrya1  = [str2 componentsSeparatedByString:@" " ];

    str2 = arrya1.firstObject;

    NSString *dateStr = [ NSString stringWithFormat:@"%@ 00:00:01",str1];

    //传入时间

    //将传入时间转化成需要的格式

    NSDateFormatter *format = [[ NSDateFormatter alloc ] init];

    [ format setDateFormat:@"yyyy-MM-dd HH:mm:ss" ];

    NSDate *fromdate = [format dateFromString:dateStr];

    NSTimeZone *fromzone = [ NSTimeZone systemTimeZone ];

    NSInteger frominterval = [fromzone secondsFromGMTForDate: fromdate];

    NSDate *fromDate = [fromdate  dateByAddingTimeInterval: frominterval];

    NSLog(@"调的时间=%@",fromDate);

    NSString *dateStr1 = [ NSString stringWithFormat : @"%@ 23:59:59",str2];

    //传入时间

    //将传入时间转化成需要的格式

    NSDateFormatter *format1 = [[ NSDateFormatter alloc ] init ];

    [format1 setDateFormat : @"yyyy-MM-dd HH:mm:ss" ];

    NSDate *fromdate1 = [format1 dateFromString : dateStr1];

    NSTimeZone *fromzone1 = [ NSTimeZone systemTimeZone ];

    NSInteger frominterval1 = [fromzone1 secondsFromGMTForDate : fromdate1];

    NSDate *fromDate1 = [fromdate1  dateByAddingTimeInterval : frominterval1];

    NSLog(@"调的时间1=%@",fromDate1);

    double intervalTime = [fromDate1 timeIntervalSinceReferenceDate ] - [fromDate timeIntervalSinceReferenceDate ];

    long lTime = (long)intervalTime;

    NSInteger iDays = lTime/60/60/24;

    if (iDays <= 0 ) {

      return NO;

    }else{

        return YES;

    }

}

//感谢大神的代码，拷贝为了记录

比较两个NSDate类型的参数相差的时间差