时差由unix_timeStamp计算

Question

    NSTimeInterval gmtInterval = [activityDate doubleValue];

    NSDate *localCurrentDate = [NSDate dateWithTimeIntervalSince1970:gmtInterval];

    gmtInterval += [[NSTimeZone systemTimeZone] secondsFromGMT];

    localCurrentDate = [NSDate dateWithTimeIntervalSince1970:gmtInterval];
    NSLog(@"PostedDate =  %@", localCurrentDate);
    NSLog(@"Now =  %@", [NSDate date]);

    NSTimeInterval distanceBetweenDates = [localCurrentDate timeIntervalSinceNow];

您好我正在计算发布时间与当前时间之间的时差。我已使用上面的代码使用 unix_timestamp 计算发布时间。我正在计算负值中的时差。所以我记录它们错误的日期如下所示..

PostedDate =  2014-12-15 04:01:57 +0000
Now =  2014-12-18 10:54:02 +0000

应该如下所示

PostedDate =  2014-12-18 04:01:57 +0000
Now =  2014-12-18 16:27:02 +0000

我做错了什么我找不到.. 请帮我解决这个问题。