创建当前时间

NSDate *date = [NSDate date];  

从现在开始的24小时

        NSTimeInterval a_day = 24*60*60;            NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:a_day];

根据已有日期创建日期

    NSTimeInterval a_day = 24*60*60;        NSDate *date = [NSDate date];        NSDate *tomorrow = [date addTimeInterval: date];  

日期比较

   BOOL isEqual = [date isEqualToDate:tomorrow];        f(isEqual){        NSLog(@"equal");  

//获取较早的日期

NSDate *earlier_date = [tomorrow earlierDate:date];      NSLog(@"earlierDate  = %@",earlierDate); 

//较晚的日期

    NSDate *laterDate = [tomorrow laterDate:date];        NSLog(@"laterDate  = %@",laterDate);  

//两个日期之间相隔多少秒

    NSTimeInterval secondsInterval= [date timeIntervalSinceDate:tomorrow];        NSLog(@"secondsInterval=  %lf",secondsInterval);  

 //通过NSCalendar类来创建日期

    NSDateComponents *comps = [[NSDateComponentsalloc]init];        [comps setMonth:01];        [comps setDay:31];        [comps setYear:2013];        NSCalendar *calendar = [[NSCalendaralloc]initWithCalendarIdentifier:NSGregorianCalendar];        NSDate *date = [calendar dateFromComponents:comps];  

 //从已有日期获取日期

    unsigned units  = NSMonthCalendarUnit|NSDayCalendarUnit|NSYearCalendarUnit;        NSDateComponents *_comps = [calendar components:units fromDate:date];        NSInteger month = [_comps month];        NSInteger year = [_comps year];        NSInteger day = [_comps day];        //NSDateFormatter实现日期的输出        NSDateFormatter *formatter = [[NSDateFormatteralloc]init];        [formatter setDateStyle:NSDateFormatterFullStyle];//直接输出的话是机器码        //或者是手动设置样式[formatter setDateFormat:@"yyyy-mm-dd"];        NSString *dateString = [formatter stringFromDate:date];        NSLog(@"dateString = %@",dateString);        NSLog(@"formater = %@",formatter);  

//获取日期格式对象

- (NSDateFormatter *)getDateFormatter {        if (dateFormatter == nil) {        dateFormatter = [[NSDateFormatter alloc] init];        [dateFormatter setDateStyle:NSDateFormatterMediumStyle];        [dateFormatter setTimeStyle:NSDateFormatterNoStyle];        }        return dateFormatter;    }