How to represent the current UK time?

Question

Hi,

I'm facing an issue while converting dates between my server and client where both is running in Germany. The Regional settings on the client machines could be set to both UK or Germany.I recieve a date from the server which is CET format, and I need to represent this time on UI as UK time. For example a time recieved from server like say, 01/07/2010 01:00:00 should be represented on the UI as 01/07/2010 00:00:00. I have written a converter for this purpose, however while running it 'am getting a time difference of 2 hours.Below is the code, please can you help?

public class LocalToGmtConverter : IDateConverter
{
    private readonly TimeZoneInfo timeZoneInfo;

    public LocalToGmtConverter()
        : this(TimeZoneInfo.Local)
    {

    }
    public LocalToGmtConverter(TimeZoneInfo timeZoneInfo)
    {
        this.timeZoneInfo = timeZoneInfo;
    }

    public DateTime Convert(DateTime localDate)
    {
        var utcKind = DateTime.SpecifyKind(localDate, DateTimeKind.Utc);
        return utcKind;
    }

    public DateTime ConvertBack(object fromServer)
    {
        DateTime serverDate = (DateTime)fromServer;

        var utcOffset = timeZoneInfo.GetUtcOffset(serverDate);

        var uiTime = serverDate- utcOffset;

        return uiTime;

    }
}

Answer 1

Use TimeZoneInfo.ConvertTime to convert original input timezone (CET) to target timezone (UK).

public static DateTime ConvertTime(
    DateTime dateTime,
    TimeZoneInfo sourceTimeZone,
    TimeZoneInfo destinationTimeZone
)

Full guidance on MSDN here:

Converting Times Between Time Zones

Modified code sample from MSDN:

DateTime ceTime = new DateTime(2007, 02, 01, 08, 00, 00);
try
{
   TimeZoneInfo ceZone = TimeZoneInfo.FindSystemTimeZoneById("Central Europe Standard        Time");
   TimeZoneInfo gmtZone = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");
   Console.WriteLine("{0} {1} is {2} GMT time.", 
           ceTime, 
           ceZone.IsDaylightSavingTime(ceTime) ? ceZone.DaylightName : ceZone.StandardName, 
           TimeZoneInfo.ConvertTime(ceTime, ceZone, gmtZone));
}
catch (TimeZoneNotFoundException)
{
   Console.WriteLine("The registry does not define the required timezones.");
}                           
catch (InvalidTimeZoneException)
{
   Console.WriteLine("Registry data on the required timezones has been corrupted.");
}

Answer 2

I think you're converting to UTC (instead of UK) time. Since there is still summer time in Central Europe (event if the temperatures say otherwise), the difference is +2 hours until October, 31st.

If you know that you're converting from Germany to UK (i.e. CEST to BST in summer and CET to GMT in winter), why you don't just subtract 1 hour?

If you want the time zone information for UK, you can construct it using

var britishZone = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");

Then you could convert the date using

var newDate = TimeZoneInfo.ConvertTime(serverDate, TimeZoneInfo.Local, britishZone);

Answer 3

The better approach to deal with local times is store them in unified representation such as UTC.

So you can convert all input times to UTC (via .ToUniversalTime()), and store (or transmit) its value. When you need to show it just convert back by using .ToLocalTime().

So you avoid rquirements to know which time zone was original value and can easily show stored value in different timezones.

Also you can avoid incoming troubles where you have to write specific logic for processing time in next timezone trying to figure out how to convert them amongs all available.