| public GetAmbiguousTimeOffsets ( System.DateTime dateTime ) : System.TimeSpan[] | ||
| dateTime | System.DateTime | |
| return | System.TimeSpan[] | |
public static TimeSpan GetUtcOffset(DateTime dateTime, TimeZoneInfo timeZoneInfo)
{
// Unlike the default behavior of TimeZoneInfo.GetUtcOffset, it is prefered to choose
// the DAYLIGHT time when the input is ambiguous, because the daylight instance is the
// FIRST instance, and time moves in a forward direction.
TimeSpan offset = timeZoneInfo.IsAmbiguousTime(dateTime)
? timeZoneInfo.GetAmbiguousTimeOffsets(dateTime).Max()
: timeZoneInfo.GetUtcOffset(dateTime);
return offset;
}
/// <summary>
/// Rounds the time to the start of the hour in the specified time zone.
/// </summary>
/// <param name="time">The time in UTC.</param>
/// <param name="timeZone">The time zone. (Can be <see langword="null"/>.)</param>
/// <param name="localTime">Out: The time in the specified time zone.</param>
/// <returns>
/// The start of the day in the specified time zone. The returned value is given in UTC.
/// </returns>
/// <remarks>
/// <para>
/// The method returns <paramref name="time"/> unchanged if <paramref name="timeZone"/> is
/// <see cref="TimeZoneInfo.Utc"/> or <see langword="null"/>.
/// </para>
/// <para>
/// <strong>Important:</strong> The returned <paramref name="localTime"/> is valid (i.e. has
/// an equivalent in UTC), but it may be ambiguous (i.e. has more than one equivalent in
/// UTC)!
/// </para>
/// </remarks>
private static DateTime RoundToHour(DateTime time, TimeZoneInfo timeZone, out DateTime localTime)
{
Debug.Assert(time.Kind == DateTimeKind.Utc, "Time is expected to be UTC.");
if (timeZone == null || timeZone.Equals(TimeZoneInfo.Utc))
{
localTime = time;
return time;
}
// Convert time to specified time zone.
localTime = TimeZoneInfo.ConvertTime(time, timeZone);
// Add half an hour for rounding.
localTime = localTime.AddMinutes(30);
#if SILVERLIGHT
// Silverlight supports only conversion Local <-> UTC:
localTime = new DateTime(localTime.Year, localTime.Month, localTime.Day, localTime.Hour, 0, 0, DateTimeKind.Local);
while (timeZone.IsInvalidTime(localTime))
localTime = localTime.AddHours(1);
// When switching back from Daylight Saving Time to normal time, the time in the
// local time zone is ambiguous and can be mapped to different time values in UTC.
if (timeZone.IsAmbiguousTime(localTime))
{
// Map the local time to the time in UTC which is closest to the original value.
TimeSpan[] offsets = timeZone.GetAmbiguousTimeOffsets(localTime);
TimeSpan minDistance = TimeSpan.MaxValue;
DateTime closestTime = new DateTime();
foreach (var offset in offsets)
{
DateTime timeUtc = localTime - offset;
TimeSpan distance = (timeUtc - time).Duration();
if (distance < minDistance)
{
minDistance = distance;
closestTime = timeUtc;
}
}
time = DateTime.SpecifyKind(closestTime, DateTimeKind.Utc);
}
else
{
time = TimeZoneInfo.ConvertTime(localTime, TimeZoneInfo.Utc);
}
#else
localTime = new DateTime(localTime.Year, localTime.Month, localTime.Day, localTime.Hour, 0, 0);
while (timeZone.IsInvalidTime(localTime))
localTime = localTime.AddHours(1);
// When switching back from Daylight Saving Time to normal time, the time in the
// local time zone is ambiguous and can be mapped to different time values in UTC.
if (timeZone.IsAmbiguousTime(localTime))
{
// Map the local time to the time in UTC which is closest to the original value.
TimeSpan[] offsets = timeZone.GetAmbiguousTimeOffsets(localTime);
TimeSpan minDistance = TimeSpan.MaxValue;
DateTime closestTime = new DateTime();
foreach (var offset in offsets)
{
DateTime timeUtc = localTime - offset;
TimeSpan distance = (timeUtc - time).Duration();
if (distance < minDistance)
{
minDistance = distance;
closestTime = timeUtc;
}
}
time = DateTime.SpecifyKind(closestTime, DateTimeKind.Utc);
}
else
{
time = TimeZoneInfo.ConvertTime(localTime, timeZone, TimeZoneInfo.Utc);
}
#endif
return time;
}
