Europe/London time on Blazor Wasm

Question

I've read the docs on timezone updates in .net 6, but I'm failing to understand something!

I want to get the number of hours between "now" (my time) and 10pm tonight (London time).

TimeRemaining = _date.Subtract(DateTime.Now);

With _date being, 10pm tonight (London time).

However DateTime.Now returns a time in UTC, and given we've now moved to BST we're an hour out.

I am trying to use the TimeZoneInfo to get the relevant timezone, however:

TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time") // "The time zone ID 'GMT Standard Time' was not found on the local computer."
TimeZoneInfo.FindSystemTimeZoneById("Europe/London") // "The time zone ID 'Europe/London' was not found on the local computer."

There doesn't appear to be a way to get the time currently in London (taking in to account daylight savings changes etc), but the docs suggest there should be! What am I missing?

Answer 1

I just tried the following in a Blazor WebAssembly project, inside a .razor file, and it worked just fine:

@code {

    static TimeSpan GetTimeUntil10PMLondon()
    {
        var london = TimeZoneInfo.FindSystemTimeZoneById("Europe/London");
        var time = new TimeOnly(22, 0); // 22:00 = 10:00PM
        var nextTime = GetNextTimeInZone(time, london);
        return nextTime - DateTimeOffset.UtcNow;
    }

    static DateTimeOffset GetNextTimeInZone(TimeOnly time, TimeZoneInfo timeZone)
    {
        // get the time specified, on today's date in the specified time zone
        var now = DateTimeOffset.UtcNow;
        var date = DateOnly.FromDateTime(TimeZoneInfo.ConvertTime(now, timeZone).Date);
        var timeToday = GetDateTimeOffset(date, time, timeZone);

        // return the time today, if it hasn't passed yet
        if (now < timeToday)
            return timeToday;

        // otherwise, return the time tomorrow
        return GetDateTimeOffset(date.AddDays(1), time, timeZone);
    }

    static DateTimeOffset GetDateTimeOffset(DateOnly date, TimeOnly time, TimeZoneInfo timeZone)
    {
        var dateTime = date.ToDateTime(time);
        var offset = timeZone.GetUtcOffset(dateTime);
        return new DateTimeOffset(dateTime, offset);
    }
}

@GetTimeUntil10PMLondon()

You had said that TimeZoneInfo.FindSystemTimeZoneById("Europe/London") didn't work, but it should, and does for me. Perhaps you are not on the current version? This was updated in .NET 6.