Your UTCToLocal looks like it's doing more work than it needs to, to be honest.
It should just be:
// Note: the DateTime here must have a "Kind" of Utc.
public static DateTime UTCtoLocal(this DateTime dateTime)
{
Instant instant = Instant.FromDateTimeUtc(dateTime);
IDateTimeZoneProvider timeZoneProvider = DateTimeZoneProviders.Tzdb;
var usersTimezoneId = "Europe/London"; //just an example
var usersTimezone = timeZoneProvider[usersTimezoneId];
var usersZonedDateTime = instant.InZone(usersTimezone);
return usersZonedDateTime.ToDateTimeUnspecified();
}
Similarly your LocalToUTC should be along these lines:
// The DateTime here should have a "Kind" of Unspecified
public static DateTime LocaltoUTC(this DateTime dateTime)
{
LocalDateTime localDateTime = LocalDateTime.FromDateTime(dateTime);
IDateTimeZoneProvider timeZoneProvider = DateTimeZoneProviders.Tzdb;
var usersTimezoneId = "Europe/London";
var usersTimezone = timeZoneProvider[usersTimezoneId];
var zonedDbDateTime = usersTimezone.AtLeniently(localDateTime);
return zonedDbDateTime.ToDateTimeUtc();
}
You don't need to convert it to a different time zone: ZonedDateTime
knows what the instant is, and ToDateTimeUtc
will do the right thing. Note that there's no real dateTimeFromDb
here, because if you're converting from an unspecified DateTime
, that's presumably from the user...