获取夏令时转换发生的下一个日期/时间

Question

我想在C#中编写(或使用它,如果它已经退出)一个函数,它返回给定System.TimeZoneInfo对象的下一个DST转换的日期/时间以及该时区中特定的"截至"时间.返回的时间应该在提供的时区内.我想要的功能有这个签名:

public DateTime GetNextTransition(DateTime asOfTime, TimeZoneInfo timeZone)
{
    // Implement me!
}

例如,如果我传入"东部标准时间"TimeZoneInfo对象,以及1/21/2011 @ 17:00作为"asOfTime",我希望此函数返回2011年3月13日@ 2:00.

该System.TimeZoneInfo.TransitionTime结构似乎有我需要的所有信息,但理想会有某种内在的机制的规则转换为实际日期.有人有什么建议吗？

Answer 1

看看这个页面上的例子,我认为它会得到你需要的东西.

MSDN - TransitionTime

Answer 2

你好呀。可能为时已晚，但我将在此处发布我用于此目的的代码。这可能会节省某人的时间来实施它。我实际上是在 @Jamiegs 答案链接的帮助下完成的。

    public static DateTime? GetNextTransition(DateTime asOfTime, TimeZoneInfo timeZone)
    {
        TimeZoneInfo.AdjustmentRule[] adjustments = timeZone.GetAdjustmentRules();
        if (adjustments.Length == 0)
        {
            // if no adjustment then no transition date exists
            return null;
        }

        int year = asOfTime.Year;
        TimeZoneInfo.AdjustmentRule adjustment = null;
        foreach (TimeZoneInfo.AdjustmentRule adj in adjustments)
        {
            // Determine if this adjustment rule covers year desired
            if (adj.DateStart.Year <= year && adj.DateEnd.Year >= year)
            {
                adjustment = adj;
                break;
            }
        }

        if (adjustment == null)
        {
            // no adjustment found so no transition date exists in the range
            return null;
        }


        DateTime dtAdjustmentStart = GetAdjustmentDate(adjustment.DaylightTransitionStart, year);
        DateTime dtAdjustmentEnd = GetAdjustmentDate(adjustment.DaylightTransitionEnd, year);


        if (dtAdjustmentStart >= asOfTime)
        {
            // if adjusment start date is greater than asOfTime date then this should be the next transition date
            return dtAdjustmentStart;
        }
        else if (dtAdjustmentEnd >= asOfTime)
        {
            // otherwise adjustment end date should be the next transition date
            return dtAdjustmentEnd;
        }
        else
        {
            // then it should be the next year's DaylightTransitionStart

            year++;
            foreach (TimeZoneInfo.AdjustmentRule adj in adjustments)
            {
                // Determine if this adjustment rule covers year desired
                if (adj.DateStart.Year <= year && adj.DateEnd.Year >= year)
                {
                    adjustment = adj;
                    break;
                }
            }

            dtAdjustmentStart = GetAdjustmentDate(adjustment.DaylightTransitionStart, year);
            return dtAdjustmentStart;
        }
    }


    public static DateTime GetAdjustmentDate(TimeZoneInfo.TransitionTime transitionTime, int year)
    {
        if (transitionTime.IsFixedDateRule)
        {
            return new DateTime(year, transitionTime.Month, transitionTime.Day);
        }
        else
        {
            // For non-fixed date rules, get local calendar
            Calendar cal = CultureInfo.CurrentCulture.Calendar;
            // Get first day of week for transition
            // For example, the 3rd week starts no earlier than the 15th of the month
            int startOfWeek = transitionTime.Week * 7 - 6;
            // What day of the week does the month start on?
            int firstDayOfWeek = (int)cal.GetDayOfWeek(new DateTime(year, transitionTime.Month, 1));
            // Determine how much start date has to be adjusted
            int transitionDay;
            int changeDayOfWeek = (int)transitionTime.DayOfWeek;

            if (firstDayOfWeek <= changeDayOfWeek)
                transitionDay = startOfWeek + (changeDayOfWeek - firstDayOfWeek);
            else
                transitionDay = startOfWeek + (7 - firstDayOfWeek + changeDayOfWeek);

            // Adjust for months with no fifth week
            if (transitionDay > cal.GetDaysInMonth(year, transitionTime.Month))
                transitionDay -= 7;

            return new DateTime(year, transitionTime.Month, transitionDay, transitionTime.TimeOfDay.Hour, transitionTime.TimeOfDay.Minute, transitionTime.TimeOfDay.Second);
        }
    }

示例用法如下：

// This should give you DateTime object for date 26 March 2017 
// because this date is first transition date after 1 January 2017 for Central Europe Standard Time zone
DateTime nextTransitionDate = GetNextTransition(new DateTime(2017, 1, 1), TimeZoneInfo.FindSystemTimeZoneById("Central Europe Standard Time"))

您可以在这里找到我使用的代码。

Answer 3

System.TimeZoneInfo.TransitionTime 看起来像是一个可以保存此类时间转换数据的结构，而不是计算实际值的函数。要创建这样的函数，我会在某处在线查找数据，然后使用静态 CreateFloatingDateRule 或 CreateFixedDateRule 方法创建值。