DateTime比较忽略类型吗? [英] DateTime Compare Ignores Kind?

问题描述

DateTime d1=new DateTime(2015, 1, 1, 0, 0, 0, DateTimeKind.Utc);
DateTime d2=new DateTime(2015, 1, 1, 0, 0, 0, DateTimeKind.Local);
Console.WriteLine(d1==d2);           // prints true
Console.WriteLine(d1<d2);            // prints false
Console.WriteLine(d1.CompareTo(d2)); // prints 0
Console.WriteLine(d1.ToUniversalTime()==d2.ToUniversalTime()); // prints false

对我来说，这似乎是个错误，如果不是让我惊讶的话.

This looks like a bug to me, if not color me surprised.

对于每个比较，我都必须调用ToUniversalTime()还是有更好的选择?

Do I have to call ToUniversalTime() for every comparison or is there a better alternative?

如何避免由于诸如DateTimeKind.Unspecified而忘记调用ToUniversalTime()或得到错误结果的陷阱?

How do you avoid pitfalls like forgetting to call ToUniversalTime() or getting a wrong result because of DateTimeKind.Unspecified?

推荐答案

MSDN文档非常清楚，没有使用Equality运算符将 DateTimeKind 考虑在内.

The MSDN documentation is quite clear that DateTimeKind is not taken into account using the Equality operator.

Equality运算符通过比较两个滴答数来确定两个DateTime值是否相等.在比较DateTime对象之前，请确保这些对象表示同一时区中的时间.您可以通过比较其Kind属性的值来完成此操作.

MSDN-DateTime.平等算子

您可以编写自己的扩展方法以包括 DateTimeKind 比较:

You could write your own extension method to include the DateTimeKind comparison:

public static bool EqualsWithKind(this DateTime time, DateTime other)
{
      return time.Kind == other.Kind &&
             time == other;
}

考虑到 Panagiotis Kanavos 和 James Thorpe 关于 DateTimeOffset 的评论:

在保证偏移量与本地偏移量相同的情况下使用.

Use if the offsets are guaranteed to be the same as the local offset.

public static bool EqualsWithTimezone(this DateTime time, DateTime other)
{
      return new DateTimeOffset(time) == new DateTimeOffset(other);
}

如果偏移量不能保证相同，则使用:

Use if the offsets are NOT guaranteed to be the same:

public static bool EqualsInclTimezone(this DateTime time, TimeSpan timeOffset, DateTime other, TimeSpan otherOffset)
{
      return new DateTimeOffset(time, timeOffset) == new DateTimeOffset(other, otherOffset);
}

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