Determine how to calculate times across different

问题:

When converting times between time zones. I found the follow code works. However I am not sure how programmatically what to put as my offset for the constructor for the ZonedDateTime. I had a choice of one of the offsets on zoneChicago, which is just two, because its either with our without daylight savings, but how do I know which one I use, and for timezones that have more then just two, what is the best way to populate that offset?

Thanks,

Jim

var zoneLA      = c.GetZoneOrNull("America/Los_Angeles");
var zoneChicago = c.GetZoneOrNull("America/Chicago");

var zdtChicago = new ZonedDateTime( LocalDateTime.FromDateTime(DateTime.Now)
                                  , zoneChicago
                                  , zoneChicago.MaxOffset);

var zdtLA = zdtChicago.WithZone(zoneLA);

回答1:

If you're interested in the current time, you can make this much simpler - and indeed more testable. Make your code take an IClock as a "service for providing the current instant in time". For the concrete implementation, use SystemClock.Instance in production, but FakeClock for testing.

IClock has a single member: Now. That returns the current Instant in time, which isn't tied to a time zone or even a calendar system.

With an Instant and a time zone, you can easily get to a ZonedDateTime:

Instant now = clock.Now;
var zone = DateTimeZoneProviders.Tzdb["America/Los_Angeles"];
ZonedDateTime = now.InZone(zone);

It will work out what the local date/time and offset is. You don't need to do anything clever :)