get DateTimeOffset from DateTime (utc) and TimeZoneInfo

Question

I need to convert DateTime+TimeZoneInfo into DateTimeOffset.

How do I do this? I assume I have to pass TimeSpan but then I'm not sure if daylight saving times will be handled properly..

Thanks!

UPDATE

TimeZoneInfo timeZone = TimeZoneInfo.FindSystemTimeZoneById("Mountain Standard Time");
return new DateTimeOffset(DateTime.UtcNow, timeZone.BaseUtcOffset);

This code throws exception..

The UTC Offset for Utc DateTime instances must be 0.\r\nParameter name: offset

UPDATE 2

Sorry, I didn't realize that DateTimeOffset contains only offset, it doesn't contain actual zone information - so I'm accepting answer from @Dave as it is what I will be using..

Answer 1

You should be about to get the difference between DateTime.UtcNow and DateTime.Now

var now = DateTime.Now;
var utcNow = now.ToUniversalTime();
var ts = utcNow - now;

If you are saving the offset, it is usually beneficial to save all dates in UTC (especially in a db) so you won't have to deal with offsets. You simply convert them before displaying but do all calculations in UTC.

Edit: If you have a TimeZone object, you can convert a UTC date to the local time for that time zone.

TimeZone.CurrentTimeZone.ToLocalTime()

OR

DateTime dt = TimeZoneInfo.ConvertTimeFromUtc()

Here's some sample code that will list a date in all timezones.

var dt = new DateTime(2011, 5, 21, 11, 0, 0);
foreach (var tzi in TimeZoneInfo.GetSystemTimeZones())
{
    Console.WriteLine(string.Format("Time in {0} is {1}", tzi.DisplayName, TimeZoneInfo.ConvertTimeFromUtc(dt, tzi)));
}

Answer 2

TimeZoneInfo has a BaseUtcOffset property that is a TimeSpan representing the offset.

This is the offset that the DateTimeOffset constructors expects:

var myDTOffset = new DateTimeOffset(myDatetime, mytzInfo.BaseUtcOffset);

Answer 3

I think there may be an easier solution to eliminate the error. You tried:

TimeZoneInfo timeZone = TimeZoneInfo.FindSystemTimeZoneById("Mountain Standard Time");
return new DateTimeOffset(DateTime.UtcNow, timeZone.BaseUtcOffset);

DateTimeOffset throws an exception. What you wanted is this:

TimeZoneInfo timeZone = TimeZoneInfo.FindSystemTimeZoneById("Mountain Standard Time");
return new DateTimeOffset(DateTime.UtcNow).ToOffset(timeZone.BaseUtcOffset);

This will not throw the exception. I'm not sure why the constructor that accepts a TimeSpan even exists, since it only works if it matches the local or utc offset given in the DateTime object. But it is still possible with less headache.