objective-c - 如何从 NSDate 中减去持续时间，但不包括周末？

Question

以今天为例，如何判断是230个工作日之前的日期？

我知道如何使用 while 循环检查日期并在工作日减去 1 来迭代执行此操作，但我想知道是否有更好的方法。

另外，我们以周日下午 1 点为例，从该时间减去 3 个工作日和 2 小时。首先，从周末减去工作时间没有意义。所以它必须将时间移到星期五的 23:59:59，然后减去这 3 天 2 小时。

如果是星期一凌晨 1:30，我从那个时间减去 5 天和 3 个工作小时，那么结果应该是前一周的星期五下午 22:30。

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测试凯文方法的代码:

NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *dc = [[NSDateComponents new] autorelease];
dc.month = 12;
dc.day = 19;
dc.year = 2011;
dc.hour = 1;
dc.minute = 0;
dc.second = 0;

NSDate *date = [cal dateFromComponents:dc];

NSLog(@"%@", [date descriptionWithCalendarFormat:nil timeZone:nil locale:nil]);
date = dateBySubtractingWorkOffset(date, 0, 2);
NSLog(@"%@", [date descriptionWithCalendarFormat:nil timeZone:nil locale:nil]);

输出日志:

2011-12-02 16:33:46.878 otest[7124:707] 2011-12-19 01:00:00 -0500
2011-12-02 16:33:47.659 otest[7124:707] 2011-12-18 23:00:00 -0500

它永远不应该是 12-18，因为那是星期天。

Answer 1

算出你约会的最后一个周末有多长，从你的日期和你的偏移量中减去那个数额。现在您可以将您的偏移量除以 5 以计算出您的偏移量中有多少周，然后将其乘以 7 并从您的日期中减去这个新值。取你之前的偏移量(你除以 5 的那个)并将它除以 5，以获得剩余天数。如果它大于 0，请从您的日期中减去偏移量 + 2(周末)。

请注意，这假设每个工作日都是工作日。公司假期往往会使该假设无效。如果您需要处理假期，就会遇到更棘手的问题。

更新:这里尝试修复 David 的代码以实际表达这里的想法:

NSDate *dateBySubtractingWorkOffset(NSDate *date, NSUInteger days, NSUInteger hours) {
    const int secsInHour = 60*60;
    const int secsInDay = 24*secsInHour;
    NSTimeInterval offset = days*secsInDay + hours*secsInHour;
    NSCalendar *cal = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];

    // figure out distance from last weekend
    {
        NSUInteger units = NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSWeekdayCalendarUnit;
        NSDateComponents *dc = [cal components:units fromDate:date];
        if (dc.weekday == 1 || dc.weekday == 7) {
            // we're in the weekend already. Let's just back up until friday
            // and then we can start our calculations there
        } else {
            // figure out our offset from sunday 23:59:59
            dc.day -= (dc.weekday - 1);
            dc.weekday = 1;
            dc.hour = 23;
            dc.minute = 23;
            dc.second = 23;
            NSDate *sunday = [cal dateFromComponents:dc];
            NSTimeInterval newOffset = [date timeIntervalSinceDate:sunday];
            if (offset < newOffset) {
                // our offset doesn't even go back to sunday, we don't need any calculations
                return [date dateByAddingTimeInterval:-offset];
            }
            offset -= [date timeIntervalSinceDate:sunday];
            // Now we can jump back to Friday with our new offset
        }
        // Calculate last friday at 23:59:59
        dc.day -= (dc.weekday % 7 + 1);
        dc.hour = 23;
        dc.minute = 59;
        dc.second = 59;
        date = [cal dateFromComponents:dc];
    }

    // We're now set to Friday 23:59:59
    // Lets figure out how many weeks we have
    int secsInWorkWeek = 5*secsInDay;
    NSInteger weeks = (NSInteger)trunc(offset / secsInWorkWeek);
    offset -= weeks*secsInWorkWeek;
    if (weeks > 0) {
        // subtract that many weeks from the date
        NSDateComponents *dc = [[NSDateComponents alloc] init];
        dc.week = -weeks;
        date = [cal dateByAddingComponents:dc toDate:date options:0];
        [dc release];
    }
    // now we can just subtract our remaining offset from the date
    return [date dateByAddingTimeInterval:-offset];
}