NSDate 的一些操作（比较、创建、在现有date加减一定时间等）

人懒，就不自己归纳总结了，别人总结的挺好，拷贝一下，备用

转载地址：http://blog.csdn.net/reylen/article/details/8560128

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;
 }