我使用以下代码来显示2005年至2035年之间的夏令时。
对于2005年，此page显示DST在4月3日至10月30日之间。但是GetDaylightChanges返回3月13日和11月6日。
.NET GetDaylightChanges是可靠的功能吗？
public static void GetCurrentTimeZone()
{
for (int i = 0; i < 30; i++)
{
var dlt = TimeZone.CurrentTimeZone.GetDaylightChanges(2005 + i);
Console.WriteLine(2005 + i);
Console.WriteLine(dlt.Start.ToLongDateString());
Console.WriteLine(dlt.End.ToLongDateString());
Console.WriteLine(" ");
}
}
最佳答案
从1987-2006年，规则是：DST从4月的第一个星期日到10月的最后一个星期日生效。
从2007年至今，规则是：DST从3月的第二个星期日到11月的第一个星期日生效。
但是，正如@MaheshKava指出的那样，GetDaylightChanges API的备注部分指出：
因为TimeZone类仅支持一个夏令时
调整规则，GetDaylightChanges方法将应用当前
调整规则适用于任何年份，无论调整规则是否
实际上适用于该年。
这意味着当前的规则（3月的第二个星期日至11月的第一个星期日）将一直适用于所有年份，无论该规则在该年实际上是否有效。因此，总而言之，GetDaylightChanges将为您提供2007年之前任何一年的不准确结果，这显然是设计使然。
API文档进一步说，您可以使用TimeZoneInfo.GetAdjustmentRules获得更准确的信息。我对此感到很好奇，因此我编写了以下代码：
static void Main(string[] args)
{
PrintAllDaylightSavingsAdjustmentDates();
Console.ReadLine();
}
public static void PrintAllDaylightSavingsAdjustmentDates()
{
TimeZoneInfo timeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");
TimeZoneInfo.AdjustmentRule[] adjustmentRules = timeZoneInfo.GetAdjustmentRules();
for (int year = 2000; year < 2030; year++)
{
PrintDaylightSavingsAdjustmentDatesForYear(adjustmentRules, year);
}
}
public static void PrintDaylightSavingsAdjustmentDatesForYear
(
TimeZoneInfo.AdjustmentRule[] adjustmentRules,
int year
)
{
DateTime firstOfYear = new DateTime(year, 1, 1);
foreach (TimeZoneInfo.AdjustmentRule adjustmentRule in adjustmentRules)
{
if ((adjustmentRule.DateStart <= firstOfYear) && (firstOfYear <= adjustmentRule.DateEnd))
{
Console.WriteLine("In {0}, DST started on {1} and ended on {2}.",
year,
GetTransitionDate(adjustmentRule.DaylightTransitionStart, year).ToString("MMMM dd"),
GetTransitionDate(adjustmentRule.DaylightTransitionEnd, year).ToString("MMMM dd"));
}
}
}
public static DateTime GetTransitionDate
(
TimeZoneInfo.TransitionTime transitionTime,
int year
)
{
if (transitionTime.IsFixedDateRule)
{
return new DateTime(year, transitionTime.Month, transitionTime.Day);
}
else
{
if (transitionTime.Week == 5)
{
// Special value meaning the last DayOfWeek (e.g., Sunday) in the month.
DateTime transitionDate = new DateTime(year, transitionTime.Month, 1);
transitionDate = transitionDate.AddMonths(1);
transitionDate = transitionDate.AddDays(-1);
while (transitionDate.DayOfWeek != transitionTime.DayOfWeek)
{
transitionDate = transitionDate.AddDays(-1);
}
return transitionDate;
}
else
{
DateTime transitionDate = new DateTime(year, transitionTime.Month, 1);
transitionDate = transitionDate.AddDays(-1);
for (int howManyWeeks = 0; howManyWeeks < transitionTime.Week; howManyWeeks++)
{
transitionDate = transitionDate.AddDays(1);
while (transitionDate.DayOfWeek != transitionTime.DayOfWeek)
{
transitionDate = transitionDate.AddDays(1);
}
}
return transitionDate;
}
}
}
它吐出以下输出：
In 2000, DST started on April 02 and ended on October 29.
In 2001, DST started on April 01 and ended on October 28.
In 2002, DST started on April 07 and ended on October 27.
In 2003, DST started on April 06 and ended on October 26.
In 2004, DST started on April 04 and ended on October 31.
In 2005, DST started on April 03 and ended on October 30.
In 2006, DST started on April 02 and ended on October 29.
In 2007, DST started on March 11 and ended on November 04.
In 2008, DST started on March 09 and ended on November 02.
In 2009, DST started on March 08 and ended on November 01.
In 2010, DST started on March 14 and ended on November 07.
In 2011, DST started on March 13 and ended on November 06.
In 2012, DST started on March 11 and ended on November 04.
In 2013, DST started on March 10 and ended on November 03.
In 2014, DST started on March 09 and ended on November 02.
In 2015, DST started on March 08 and ended on November 01.
In 2016, DST started on March 13 and ended on November 06.
In 2017, DST started on March 12 and ended on November 05.
In 2018, DST started on March 11 and ended on November 04.
In 2019, DST started on March 10 and ended on November 03.
In 2020, DST started on March 08 and ended on November 01.
In 2021, DST started on March 14 and ended on November 07.
In 2022, DST started on March 13 and ended on November 06.
In 2023, DST started on March 12 and ended on November 05.
In 2024, DST started on March 10 and ended on November 03.
In 2025, DST started on March 09 and ended on November 02.
In 2026, DST started on March 08 and ended on November 01.
In 2027, DST started on March 14 and ended on November 07.
In 2028, DST started on March 12 and ended on November 05.
In 2029, DST started on March 11 and ended on November 04.