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; }