计算设定时间点与当前时间差的代码

 利用时间戳来准确计算某个时间点具现在的时间差，可以参考 CocoaChina 会员 “” 分享的下面这段代码- (NSString *)intervalSinceNow: (NSString *) theDate {        NSDateFormatter *date=[[NSDateFormatter alloc] init];    [date setDateFormat:@"yyyy-MM-dd HH:mm:ss"];    NSDate *d=[date dateFromString:theDate];        NSTimeInterval late=[d timeIntervalSince1970]*1;            NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];    NSTimeInterval now=[dat timeIntervalSince1970]*1;    NSString *timeString=@"";        NSTimeInterval cha=now-late;        if (cha/3600<1) {        timeString = [NSString stringWithFormat:@"%f", cha/60];        timeString = [timeString substringToIndex:timeString.length-7];        timeString=[NSString stringWithFormat:@"%@分钟前", timeString];            }    if (cha/3600>1&&cha/86400<1) {        timeString = [NSString stringWithFormat:@"%f", cha/3600];        timeString = [timeString substringToIndex:timeString.length-7];        timeString=[NSString stringWithFormat:@"%@小时前", timeString];    }    if (cha/86400>1)    {        timeString = [NSString stringWithFormat:@"%f", cha/86400];        timeString = [timeString substringToIndex:timeString.length-7];        timeString=[NSString stringWithFormat:@"%@天前", timeString];            }    [date release];    return timeString;}