将没有时区信息的DateTime解析为特定的时区

Question

This is a follow on from a question answered yesterday..

Convert 12hr Time String to DateTime object

Those times in the xml feed are EST (who does that?) but our timezone is BST.

so 10:30PM is 02:30AM UTC or 03:30AM BST

However, TryParseExact yields 10:30PM in local time (as to be expected given that there is not timezone information)

So the question; how can I parse that time as 02:30AM UTC rather than 10:30PM BST?

Answer 1

However, TryParseExact yields 10:30PM in local time

No, it doesn't. Not unless you tell it to. By default, and unless there's any indication of the offset in the pattern, the parse methods will return DateTime values with a Kind of Unspecified - which is entirely appropriate as no information has been specified. If you just convert it to a string, it will assume it's actually a local time, but that's not what the value itself says. You need to understand the three kinds of DateTime - it's a broken model IMO , but that's what we've got in the BCL.

You can pass that to the appropriate TimeZoneInfo to apply a specific time zone and get an appropriate DateTimeOffset , although it's then up to you to remember the actual time zone involved. (An offset isn't the same as a time zone.)

Alternatively, you could use my Noda Time project, which differentiates between the different logical types rather more clearly. You'd parse as a LocalTime , then decide which LocalDate to join that with in order to produce LocalDateTime , which you could then convert to a ZonedDateTime using the "America/Los_Angeles" time zone (or the Windows equivalent; the choice is yours). In performing that conversion, you'd specify what you'd want to happen if the given local time was invalid or ambiguous due to daylight saving transitions.