“半月”加多少天

Question

我有一个名为 PaymentFrequency 的枚举类型，其值表示每年进行的付款次数... 因此，我想

public enum PaymentFrequency
{
    None             = 0,
    Annually         = 1,
    SemiAnnually     = 2,
    EveryFourthMonth = 3,
    Quarterly        = 4,
    BiMonthly        = 6,
    Monthly          = 12,
    EveryFourthWeek  = 13,
    SemiMonthly      = 24,
    BiWeekly         = 26,
    Weekly           = 52
}

根据 NumberOfPayments、PaymentFrequency 和 FirstPaymentDate（DateTimeOffset 类型）计算 LastPaymentDate。但我在计算半月一次的情况下要添加多少个时间单位（天、月）时遇到问题...

    switch (paymentFrequency)
    {
        // add years...
        case PaymentFrequency.Annually:
            LastPaymentDate = FirstPaymentDate.AddYears(NumberOfPayments - 1); 
            break;
        // add months...
        case PaymentFrequency.SemiAnnually:
            LastPaymentDate = FirstPaymentDate.AddMonths((NumberOfPayments - 1) * 6); // 6 months
            break;
        case PaymentFrequency.EveryFourthMonth:
            LastPaymentDate = FirstPaymentDate.AddMonths((NumberOfPayments - 1) * 4); // 4 months
            break;
        case PaymentFrequency.Quarterly:
            LastPaymentDate = FirstPaymentDate.AddMonths((NumberOfPayments - 1) * 3); // 3 months
            break;
        case PaymentFrequency.BiMonthly:
            LastPaymentDate = FirstPaymentDate.AddMonths((NumberOfPayments - 1) * 2); // 2 months
            break;
        case PaymentFrequency.Monthly:
            LastPaymentDate = FirstPaymentDate.AddMonths(NumberOfPayments - 1);
            break;
        // add days...
        case PaymentFrequency.EveryFourthWeek:
            LastPaymentDate = FirstPaymentDate.AddDays((NumberOfPayments - 1) * 4 * 7); // 4 weeks (1 week = 7 days)
            break;
        case PaymentFrequency.SemiMonthly:
            // NOTE: how many days in semi month? AddMonths (0.5) does not work :)
            LastPaymentDate = FirstPaymentDate.AddMonths((NumberOfPayments - 1) * 0.5); // 2 weeks (1 week = 7 days)
            break;
        case PaymentFrequency.BiWeekly:
            LastPaymentDate = FirstPaymentDate.AddDays((NumberOfPayments - 1) * 2 * 7); // 2 weeks (1 week = 7 days)
            break;
        case PaymentFrequency.Weekly:
            LastPaymentDate = FirstPaymentDate.AddDays((NumberOfPayments - 1) * 7); // 1 week (1 week = 7 days)
            break;
        case PaymentFrequency.None:
        default:
            throw new ArgumentException("Payment frequency is not initialized to valid value!", "paymentFrequency");
    }

那么，使用半月时我应该使用多少天/月？ 如果不知道中间每个月的确切天数，这是否可能？ 或者这真的很简单吗？我刚刚喝完咖啡因，只见树木不见森林:)

Answer 1

对于半月付款，如果您的第一笔付款也始终是该月的第一笔付款（即从 1 日到 13 日的任何时间，如评论中所述，13 日之后开始是有问题的），您可以执行以下操作

 // assuming first payment will be 1st of month, add month for every 2 payments
 // num payments / 2 (int division, remainder is chucked)
 // then add 15 days if this is even payment of the month
 LastPaymentDate = FirstPaymentDate.AddMonths((NumberOfPayments - 1) / 2)
     .AddDays((NumberOfPayments % 2) == 0 ? 15 : 0);

：对于第一次付款，这将添加 0 个月和 0 天，因此是第一次付款日期。对于第二次付款，这将增加 0 个月（整除，余数被丢弃）和 16 号的 15 天。对于第 3 次付款，这将添加 1 个月 (1 / 3) 和下个月 1 日的 0 天，依此类推。

这是假设 FirstPaymentDate 将在某个给定月份的 1 日。如果您想让 16 日作为开始日期等，您可能可以从这里看到该去哪里。

有意义吗？

为了说明这一点，如果我们有：

DateTime LastPaymentDate, FirstPaymentDate = new DateTime(2011, 12, 5);

for(int numOfPayments=1; numOfPayments<=24; numOfPayments++)
{
    LastPaymentDate = FirstPaymentDate.AddMonths((numOfPayments - 1) / 2)
        .AddDays((numOfPayments % 2) == 0 ? 15 : 0);

    Console.WriteLine(LastPaymentDate);
}

这个循环会给我们：

12/5/2011 12:00:00 AM
12/20/2011 12:00:00 AM
1/5/2012 12:00:00 AM
// etc...
10/20/2012 12:00:00 AM
11/5/2012 12:00:00 AM
11/20/2012 12:00:00 AM

Answer 2

由于月份的长度各不相同，因此您不能只添加预定义的数字。您必须知道您正在处理哪个月份，然后从那里开始。

如果您知道每月 1 日和 16 日是到期日，那么最后一次付款是 12 月 16 日（假设您计算的是日历年）。

Answer 3

半月付款的基本对是：

• 1 和 16（每月的 1 号和 16 日）
• 15 和（2|3）？ （每月15日和最后一天）

查看并选择

Answer 4

我最近遇到了同样的问题，但我需要允许任何日期输入。这有点混乱，需要重构，但这就是我到目前为止想到的。二月遇到了一些我必须解决的问题。

Date returnDate;

if (numberOfPayments % 2 == 0)
{
   returnDate = date.AddMonths(numberOfPayments / 2);

    if (date.Day == DateTime.DaysInMonth(date.Year, date.Month))//Last day of the month adjustment
    {
        returnDate = new Date(returnDate.Year, returnDate.Month, DateTime.DaysInMonth(returnDate.Year, returnDate.Month));
    }
}
else
{
    returnDate = date.Day <= 15 ? date.AddDays(15).AddMonths((numberOfPayments - 1) / 2) : date.AddDays(-15).AddMonths((numberOfPayments + 1) / 2);
    if (date.Day == DateTime.DaysInMonth(date.Year, date.Month))//Last day of the month adjustment
    {
        returnDate = new Date(returnDate.Year, returnDate.Month, 15);
    }
    else if (date.Month == 2 && date.Day == 14)
    {
        returnDate = returnDate.AddMonths(-1);
        returnDate = new Date(returnDate.Year, returnDate.Month, returnDate.Month == 2 ? 28 : 29);
    }
    else if (date.Month == 2 && date.Day == 15)
    {
        returnDate = returnDate.AddMonths(-1);
        returnDate = new Date(returnDate.Year, returnDateMonth, DateTime.DaysInMonth(returnDate.Year, returnDate.Month));
    }
}

return returnDate;