NSDate

    // 当前时间创建NSDate

        NSDate *myDate = [NSDate date];

        NSLog(@"myDate = %@",myDate);

        //从现在开始的24小时

        NSTimeInterval secondsPerDay = 24*60*60;

        NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:secondsPerDay];

        NSLog(@"myDate = %@",tomorrow);

        //根据已有日期创建日期

         NSTimeInterval secondsPerDay1 = 24*60*60;

        NSDate *now = [NSDate date];

        NSDate *yesterDay = [now addTimeInterval:-secondsPerDay1];

        NSLog(@"yesterDay = %@",yesterDay);

        

        //比较日期

        BOOL sameDate = [now isEqualToDate:yesterDay];

        NSLog(@"sameDate = %lu",sameDate);

        //获取较早的日期

        NSDate *earlierDate = [yesterDay earlierDate:now];

        NSLog(@"earlierDate  = %@",earlierDate);

        //较晚的日期

        NSDate *laterDate = [yesterDay laterDate:now];

        NSLog(@"laterDate  = %@",laterDate);

        //两个日期之间相隔多少秒

        NSTimeInterval secondsBetweenDates= [yesterDay timeIntervalSinceDate:now];

        NSLog(@"secondsBetweenDates=  %lf",secondsBetweenDates);

        //通过NSCALENDAR类来创建日期

        NSDateComponents *comp = [[NSDateComponentsalloc]init];

        [comp setMonth:06];

        [comp setDay:01];

        [comp setYear:2001];

        NSCalendar *myCal = [[NSCalendaralloc]initWithCalendarIdentifier:NSGregorianCalendar];

        NSDate *myDate1 = [myCal dateFromComponents:comp];

        NSLog(@"myDate1 = %@",myDate1);

        

        //从已有日期获取日期

        unsigned units  = NSMonthCalendarUnit|NSDayCalendarUnit|NSYearCalendarUnit;

        NSDateComponents *comp1 = [myCal components:units fromDate:now];

        NSInteger month = [comp1 month];

        NSInteger year = [comp1 year];

        NSInteger day = [comp1 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 *string = [formatter stringFromDate:now];

        NSLog(@"string = %@",string);

        NSLog(@"formater = %@",formatter);