NSDate常用的日期操作

 // 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 = **;

        NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:secondsPerDay];

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

//根据已有日期创建日期

         NSTimeInterval secondsPerDay1 = **;

        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:];

        [comp setDay:];

        [comp setYear:];

        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;

    }