c# - DateTime 比较忽略类型？

Question

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

这对我来说看起来像是一个错误，如果不是的话color me surprised .

每次比较我都必须调用 ToUniversalTime() 还是有更好的选择？

您如何避免诸如忘记调用 ToUniversalTime() 或由于 DateTimeKind.Unspecified 而得到错误结果之类的陷阱？

Answer 1

MSDN 文档非常清楚，DateTimeKind 未考虑使用 Equality 运算符。

The Equality operator determines whether two DateTime values are equal by comparing their number of ticks. Before comparing DateTime objects, make sure that the objects represent times in the same time zone. You can do this by comparing the values of their Kind property.

MSDN - DateTime.Equality Operator

您可以编写自己的扩展方法以包含 DateTimeKind 比较:

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:

如果保证偏移量与本地偏移量相同，则使用。

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

如果不能保证偏移量相同，则使用:

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