Using TimeZoneInfo to convert between UTC/Specified TimeZone not working

All of our date/time data in our database is stored in UTC time. I'm trying to write a function to convert that UTC time into the user's preferred time zone (they can select their timezone in their profile so it has NOTHING to do with local settings on their computer and everything to do with which timezone they have selected from a dropdown of available c开发者_如何学JAVAhoices.

This function is in the context of a DevExpress AspxGridView event (the third party control is not relevant to the question but I thought I'd mention it):

DateTimeOffset utcTime = (DateTimeOffset)e.Value;

TimeZoneInfo destTimeZone = Helper.GetTimeZoneInfo();

DateTime modifiedDate = TimeZoneInfo
    .ConvertTimeFromUtc(utcTime.DateTime, destTimeZone);

e.DisplayText = String.Format("{0} {1}", 
                              modifiedDate.ToString("g"), 
                              destTimeZone.Abbreviation());

Helper.GetTimeZoneInfo() simply returns a TimeZoneInfo class that corresponds to the one the user selected, or defaults to "Pacific Standard Time" if they have not chosen one.

This generally works fine until I switch my system clock (which this server is running on) from today (which is Oct. 14, a DST date) to something like January 11, which is NOT DST.

The time seems to always be displayed in DST (i.e. always a 7 hour offset). No matter what I do with my system clock, I can't get the time to adjust for the extra hour.

For example, when I have my timezone set to Pacific Standard Time, for UTC time 10-10-2011 20:00:00, it is always displaying this time:

10-10-2011 13:00:00 (the DST time, offset of -7).

During non-Daylight Savings dates (standard), the time should be:

10-10-2011 12:00:00 (offset of -8).

What am I missing?

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The converted local time of a UTC time is always based on the time zone info for that UTC time... not for whatever the current time happens to be.

That is, the PST offset on Oct 10, 2011 UTC is always -7. It doesn't matter what date you are doing the conversion on.

...Or am I misunderstanding what you are asking?

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You might have a look at the e.Value.

Is the DateTimeKind for it set to DateTimeKind.Utc or is it DateTimeKind.Unspecified

If it is Unspecified, the conversion will not work correctly.

One cannot set the Kind directly. The best I have come up with is something along the lines of

// the value off the DB, but Kind is unspecified
var fromDb = new DateTime(1999,31,12)         

// convert it to a Utc version of the same date
var fromDbInUtc = new DateTime(fromDb.Ticks, DateTimeKind.Utc)

var destTimeZone = Helper.GetTimeZoneInfo();     

var local = TimeZoneInfo.ConvertFromUtc(fromDbInUtc, destTimeZone);  

Hope this helps,

Alan.