设置两个时间差为固定值

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDate *currentDate = [NSDate date];
    NSDateComponents *comps = [[NSDateComponents alloc] init];
    [comps setDay:1];//设置最大时间为：当前时间推后1天
    NSDate *maxDate = [calendar dateByAddingComponents:comps toDate:currentDate options:0];
    NSDateFormatter *formater = [[NSDateFormatter alloc] init];
    formater.dateFormat = @"yyyy-MM-dd HH:mm";
   ![](http://blog.csdn.net/sunnyboy9/article/details/49889923)

日期可以进行比较以确定大小或相等，也可以确定两个日期之间的时间间隔。两个日期的间隔时间差可以使用-timeIntervalSinceDate:方法来计算

   NSDate * now = [NSDatedate];
　　NSDate * anHourAgo = [nowdateByAddingTimeInterval:-60*60];
　　NSTimeInterval timeBetween = [nowtimeIntervalSinceDate:anHourAgo];
　　NSLog(@"%f",timeBetween);//结果：3600.000000

日期比较也可以使用-timeIntervalSinceNow方法获取和当前的时间间隔

   NSDate * anHourago = [NSDatedateWithTimeIntervalSinceNow:-60*60];
　　NSTimeInterval interval = [anHouragotimeIntervalSinceNow];
　　NSLog(@"%f",interval);//结果： -3600.000007

iOS比较日期大小默认会比较到秒

+(int)compareOneDay:(NSDate *)oneDay withAnotherDay:(NSDate *)anotherDay
{
   NSDateFormatter *dateFormatter = [[NSDateFormatteralloc]init];
   [dateFormatter setDateFormat:@"dd-MM-yyyy"];
   NSString *oneDayStr = [dateFormatter stringFromDate:oneDay];
   NSString *anotherDayStr = [dateFormatter stringFromDate:anotherDay];
   NSDate *dateA = [dateFormatter dateFromString:oneDayStr];
   NSDate *dateB = [dateFormatter dateFromString:anotherDayStr];
   NSComparisonResult result = [dateA compare:dateB];
   NSLog(@"date1 : %@, date2 : %@", oneDay, anotherDay);
   if (result == NSOrderedDescending) {
       //NSLog(@"Date1  is in the future");
       return 1;
   }
   else if (result ==NSOrderedAscending){
       //NSLog(@"Date1 is in the past");
       return -1;
   }
   //NSLog(@"Both dates are the same");
   return 0;
   
}

日期格式请传入：2013-08-05 12:12:12；如果修改日期格式，比如：2013-08-05，则将[df setDateFormat:@"yyyy-MM-dd HH:mm:ss"];修改为[df setDateFormat:@"yyyy-MM-dd"];

+(int)compareDate:(NSString*)date01 withDate:(NSString*)date02{
   int ci;
   NSDateFormatter *df = [[NSDateFormatteralloc]init];
   [df setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
   NSDate *dt1 = [[NSDatealloc]init];
   NSDate *dt2 = [[NSDatealloc]init];
   dt1 = [df dateFromString:date01];
   dt2 = [df dateFromString:date02];
   NSComparisonResult result = [dt1 compare:dt2];
   switch (result)
   {
           //date02比date01大
       caseNSOrderedAscending: ci=1;break;
           //date02比date01小
       caseNSOrderedDescending: ci=-1;break;
           //date02=date01
       case NSOrderedSame: ci=0;break;
       default: NSLog(@"erorr dates %@, %@", dt2, dt1);break;
   }
   return ci;
}

比较两个日期之间的差值

+ (instancetype)differencewithDate:(NSString*)dateString withDate:(NSString*)anotherdateString{
   {
       // _created_at == Thu Oct 16 17:06:25 +0800 2014
       // dateFormat == EEE MMM dd HH:mm:ss Z yyyy
       // NSString --> NSDate
       NSDateFormatter *fmt = [[NSDateFormatteralloc]init];
       // 如果是真机调试，转换这种欧美时间，需要设置locale
       fmt.locale = [[NSLocalealloc]initWithLocaleIdentifier:@"en_US"];
       
       // 设置日期格式（声明字符串里面每个数字和单词的含义）
       
       // E:星期几
       // M:月份
       // d:几号(这个月的第几天)
       // H:24小时制的小时
       // m:分钟
       // s:秒
       // y:年
       fmt.dateFormat =@"EEE MMM dd HH:mm:ss Z yyyy";
       
       // 微博的创建日期
       NSDate *createDate = [fmt dateFromString:dateString];
       // 当前时间
       NSDate *now = [NSDatedate];
       // 日历对象（方便比较两个日期之间的差距）
       NSCalendar *calendar = [NSCalendarcurrentCalendar];
       // NSCalendarUnit枚举代表想获得哪些差值
       NSCalendarUnit unit =NSCalendarUnitYear |NSCalendarUnitMonth |NSCalendarUnitDay |NSCalendarUnitHour |NSCalendarUnitMinute |NSCalendarUnitSecond;
       // 计算两个日期之间的差值
       NSDateComponents *cmps = [calendar components:unit fromDate:createDate toDate:now options:0];
       
       NSLog(@"%@ %@ %@", createDate, now, cmps);
       
       return cmps;
   }

比较两个日期之间某年或某月或某日或某时等的具体差值

+ (instancetype)differencewithDate:(NSString*)dateString withDate:(NSString*)anotherdateString{
    {
        
    NSDateFormatter * formatter = [[NSDateFormatteralloc]init];
    //    [formatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"];
    [formatter setDateFormat:@"yyyy-MM-dd "];
    NSDate  *date2 = [formatterdateFromString :dateString];
    NSDate  *date1 = [formatterdateFromString :anotherdateString];
    //     NSLog(@"------date1=%@   date2=%@------%@",date1, date2);
    NSCalendar *gregorian = [[NSCalendaralloc]initWithCalendarIdentifier:NSGregorianCalendar];
    unsignedint unitFlags =NSMonthCalendarUnit;//年、月、日、时、分、秒、周等等都可以
    NSDateComponents *comps = [gregoriancomponents:unitFlagsfromDate:date1toDate:date2options:0];
    int month = [compsmonth];//时间差
    NSLog(@"时间差 = %d，abs(month)=%d",month,abs(month));
        return month;
    }