Finding a user’s local time from UTC offset

4May/10Off

Finding a user’s local time from UTC offset

I answered a question over at StackOverflow, and I really liked the answer, so I thought I would share this nifty extension method:


        /// <summary>
        /// Convert a given DateTime object to a user's local time,
        /// taking into account changes in TimeZone rules.
        /// For example, if you were to perform this operation on
        /// a time now, during EST Daylight Saving, and that time falls
        /// outside the scope of Daylight Saving time, the rule will adjust accordingly.
        /// </summary>
        /// <param name="dateTime">The DateTime object</param>
        /// <param name="offset">offset from UTC</param>
        /// <returns>User's local time</returns>
        public static DateTime ConvertToLocalDateTime(this DateTime dateTime, int offset)
        {
            TimeZoneInfo destinationTimeZone = TimeZoneInfo.GetSystemTimeZones()
               .Where(x => x.BaseUtcOffset.Hours.Equals(offset)).FirstOrDefault();

            var rule = destinationTimeZone.GetAdjustmentRules().Where(x =>
                x.DateStart <= dateTime && dateTime <= x.DateEnd)
                .FirstOrDefault();

            TimeSpan baseOffset = TimeSpan.Zero;
            if (rule != null)
            {
                baseOffset -= destinationTimeZone.IsDaylightSavingTime(dateTime) ?
                    rule.DaylightDelta : TimeSpan.Zero;
            }

            DateTimeOffset dto = DateTimeOffset.Parse(dateTime.ToString());
            return new DateTime(TimeZoneInfo
                     .ConvertTimeFromUtc(dateTime,
                            destinationTimeZone).Ticks + baseOffset.Ticks);
        }

The summary basically says it all. I ran through a couple of tests with this, I'd like to know if anyone uses this and makes modifications to it!