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 = 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); 
//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; 
    }