When I check optionDate's DateTime property's DateTimeKind value, I see Unspecified, even though I set dt's DateTimeKind as UTC in below code. I expect optionDate has a DateTime which has a DateTimeKind property set to UTC. Where am I wrong here?

       var dt = new DateTime(Convert.ToInt32(optionDateInfo.dateTime.year),
            Convert.ToInt32(optionDateInfo.dateTime.month), Convert.ToInt32(optionDateInfo.dateTime.day),
            Convert.ToInt32(optionDateInfo.dateTime.hour), Convert.ToInt32(optionDateInfo.dateTime.minutes),
            0, DateTimeKind.Utc);

        var optionDate = new DateTimeOffset(dt);

CodePudding user response：

This is documented:

DateTimeOffset.DateTime

The value of the DateTime.Kind property of the returned DateTime object is DateTimeKind.Unspecified.

Note that a DateTimeOffset does not have a "kind". It has a date, time, and offset. When you pass your DateTime with kind Utc, to it, it sets its offset to 0, and its date & time to the DateTime given. At this point, your DateTimeKind is "lost".

An offset of 0 does not necessarily mean that its kind is DateTimeKind.Utc. It could be the local time in London, or somewhere in Africa too. So it can't give you a DateTime with kind Utc just because its offset is 0 either.

In addition, DateTime being able to represent 3 kinds of things is already a questionable design, and if the DateTime property can now return 3 different kinds of DateTime depending on whether offset matches the local time, is UTC, or something else, that's just even worse.

Instead, it is designed to have 3 properties that give you DateTimes with different kinds.

• DateTime gives you the date & time part of the DateTimeOffset, with kind Unspecified
• LocalDateTime converts the date & time part of the DateTimeOffset to the current timezone, and gives you a DateTime with kind Local.
• UtcDateTime converts the date & time part of the DateTimeOffset to UTC, and gives you a DateTime with kind Utc.

If you want a DateTime with kind Utc, you should use that last one.

CodePudding user response：

Use the SpecifyKind

var myUtcZeroOffset = DateTime.SpecifyKind(DateTime.UtcNow, DateTimeKind.Utc)

//If constructing a datetime offset to be not utc you can supply the offset instead
var myOffSetExplicitLocal = new DateTimeOffset(DateTime.Now, new TimeSpan(1, 0, 0));
var localDateTime = myOffSetExplicitLocal.DateTime;
var utcZeroOffSetDateTime = myOffSetExplicitLocal.UtcDateTime;

To make matters worse of cause it is a criticisable implementation from Microsoft, because Universally Coordinated Time is not a timezone but a notation, as per ISO 8601, so in fact toUTC as a concept is flawed because '2021-11-02T10:16:25.12345 01:00' is completely valid in the UTC format and UTC Zero offset, popularily called Zulu being the '2021-11-02T09:16:25.12345Z' equivalent which then gets datetimekind UTC is actually just in coordinated time the zero line around GMT latitude, but what makes it coordinated is the part which in 00:00 can be abbreviated to Z, so lots of stuff is done to mitigate the inherent conflict and with build servers and cloud providers the .Local is especially dubious, so I would recommend always to persist in ISO 8601 strings instead, unless you actually need to use them in with date operations in Your DB, in said case to name fields appropriate like DateTimeCreatedUtcZero column e.g. just my five cents of reason on the topic in general, hope it helps.