为什么 new DateTimeOffset(DateTime.Today).AddDays(4).Offset 和 new DateTimeOffset(DateTime.Today.AddDays(4)).Offset return 值不同？

Question

我目前在 UTC+1 时区。 TimeZoneInfo.Local.BaseUtcOffset returns +1.

和new DateTimeOffset(DateTime.Today).AddDays(4).Offsetreturns+1.

但是new DateTimeOffset(DateTime.Today.AddDays(4)).Offsetreturns+2!

更有趣的是，直到加上四天的偏移量是相同的。从四天开始调用 new DateTimeOffset(DateTime.Today.AddDays(x)).Offset returns +2 offset。为什么？

//Same offset +1
var offset2 = new DateTimeOffset(DateTime.Today).AddDays(7).Offset;
var offset22 = new DateTimeOffset(DateTime.Today.AddDays(7)).Offset;

//Same offset +1
var offset3 = new DateTimeOffset(DateTime.Today).AddDays(3).Offset;
var offset32 = new DateTimeOffset(DateTime.Today.AddDays(3)).Offset;

//Different offset +1 and +2
var offset4 = new DateTimeOffset(DateTime.Today).AddDays(4).Offset;
var offset42 = new DateTimeOffset(DateTime.Today.AddDays(4)).Offset;

//Different offset +1 and +2
var offset5 = new DateTimeOffset(DateTime.Today).AddDays(5).Offset;
var offset52 = new DateTimeOffset(DateTime.Today.AddDays(5)).Offset;

Answer 1

比我的评论更认真的回答...

来自 MSDN：

Because a DateTimeOffset object does not represent the date and time in a specific time zone, the AddDays method does not consider a particular time zone's adjustment rules when it performs date and time arithmetic.

因此

DateTimeOffset(DateTime.Today).AddDays(5)

不更改原始日期的时区（今天 = CET = UTC+1）

还有

DateTime.Today.AddDays(5)

给出 5 天后的当地时间 (CEST = UTC+2)。

所以

DateTimeOffset(DateTime.Today.AddDays(5))

将给出 CEST 偏移量 (UTC+2) 的时间

为什么 new DateTimeOffset(DateTime.Today).AddDays(4).Offset 和 new DateTimeOffset(DateTime.Today.AddDays(4)).Offset return 值不同？

Why do new DateTimeOffset(DateTime.Today).AddDays(4).Offset and new DateTimeOffset(DateTime.Today.AddDays(4)).Offset return different values?

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datetimeoffset