1 // 当前时间创建NSDate        NSDate *myDate = [NSDate date];        NSLog(@"myDate = %@",myDate);2 //从现在开始的24小时        NSTimeInterval secondsPerDay = 24*60*60;        NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:secondsPerDay];        NSLog(@"myDate = %@",tomorrow);3//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);  4//比较日期        BOOL sameDate = [now isEqualToDate:yesterDay];        NSLog(@"sameDate = %lu",sameDate);        4.1//获取较早的日期        NSDate *earlierDate = [yesterDay earlierDate:now];        NSLog(@"earlierDate  = %@",earlierDate);        4.2//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);  //获取日期格式对象- (NSDateFormatter *)dateFormatter {if (dateFormatter == nil) {dateFormatter = [[NSDateFormatter alloc] init];[dateFormatter setDateStyle:NSDateFormatterMediumStyle];[dateFormatter setTimeStyle:NSDateFormatterNoStyle];}return dateFormatter;}