如何为特定时区创建 TimeZone 对象？ C＃

Question

我找到了我所知道的确切的东西，它是如此简单（或应该是）：

TimeZone.GetDaylightChanges() 返回我所需要的：当夏令时开始和结束时：

为此，我想做：

TimeZoneInfo currentTimezone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneName);
TimeZone zone = new TimeZone (currentTimezone);  // Compile error here.

DaylightTime changes = zone.GetDaylightChanges();

这当然不会编译，因为 TimeZone 的构造函数不采用 TimeZoneInfo（Wtf？），我无法弄清楚如何以任何其他方式获取 DaylightTime Changes。我需要有人将“timeZoneName”设置为任何时区，并能够获取他们设置的任何时区的开始/结束日期时间。

非常重要：服务器运行（很可能）UTC，而不是“timeZoneName”中的时区

Answer 1

不幸的是，您不能像这样实例化一个新的 TimeZone 对象。不过，我相信您可以通过查看AdjustmentRules 从 TimeZoneInfo 类中获取您想要的信息。

以下是我编写的一些方法来启用您想要的功能。请参阅底部的示例用法，了解它与在当前系统时区使用 TimeZone 方法的比较。

更新

我已将代码修改为几个类以帮助计算日期，并大量借鉴了此处的示例：https://msdn.microsoft.com/en-us/library/system.timezoneinfo.transitiontime.isfixeddaterule.aspx

public static DaylightTime GetDaylightChanges(string timeZoneName, int year)
{
    TimeZoneInfo currentTimezone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneName);

    var currentRules =
        currentTimezone.GetAdjustmentRules().FirstOrDefault(rule =>
            rule.DateStart <= DateTime.Today &&
            rule.DateEnd >= DateTime.Today);

    if (currentRules != null)
    {
        var daylightStart = 
            GetTransitionDate(currentRules.DaylightTransitionStart, year);

        var daylightEnd = 
            GetTransitionDate(currentRules.DaylightTransitionEnd, year);

        return new DaylightTime(daylightStart, daylightEnd, 
            currentRules.DaylightDelta);
    }

    return null;
}

private static DateTime GetTransitionDate(TimeZoneInfo.TransitionTime transition, 
    int year)
{
    return (transition.IsFixedDateRule)
        ? new DateTime(year, transition.Month, transition.Day,
            transition.TimeOfDay.Hour, transition.TimeOfDay.Minute,
            transition.TimeOfDay.Second)
        : GetNonFixedTransitionDate(transition, year);
}

private static DateTime GetNonFixedTransitionDate(
    TimeZoneInfo.TransitionTime transition, int year)
{
    var calendar = CultureInfo.CurrentCulture.Calendar;
    int startOfWeek = transition.Week * 7 - 6;
    int firstDayOfWeek = (int) calendar.GetDayOfWeek(new DateTime(year, 
        transition.Month, 1));

    int changeDayOfWeek = (int) transition.DayOfWeek;

    int transitionDay = (firstDayOfWeek <= changeDayOfWeek) 
        ? startOfWeek + (changeDayOfWeek - firstDayOfWeek)
        : startOfWeek + (7 - firstDayOfWeek + changeDayOfWeek);

    if (transitionDay > calendar.GetDaysInMonth(year, transition.Month))
        transitionDay -= 7;

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

以下是如何使用它的示例，与使用当前的 TimeZone 方法相比：

public static void Main()
{
    var daylightTime = GetDaylightChanges("Pacific Standard Time", DateTime.Today.Year);
    var dylightTime2 = TimeZone.CurrentTimeZone.GetDaylightChanges(DateTime.Today.Year);
}