在COM端使用Variant（VT_DATE）如果你声明的成员作为对象，你应该能够传递一个DateTime或null和COM互操作应该处理它确定。有关详细信息，请参阅MSDN上的以下内容。

What about using a Variant (VT_DATE) on the COM side? If you declare the member as object, you should be able to pass a DateTime or null and COM interop should handle it ok. See the following on MSDN for more details.

将对象转换为变体