“日期无所不能”失败 [英] "Date Is Nothing" fails

问题描述

显然，Date类型的引用不能假定值Nothing，因为

以下代码失败：


Dim d As Date

.......其他代码......

如果d什么都没有那么


结束如果


那么对于Date类型的引用，Nothing的等价是什么？

apparently references of type Date can not assume the value Nothing, because
the following code fails:

Dim d As Date
.......other code......
If d Is Nothing Then

End If

so then what is the equivalent to Nothing for a reference of type Date ?

推荐答案

Date是值类型和值类型不能为null。想想另一种方式

来确定d变量是否已被赋予特定值。

" John A Grandy" < johnagrandy-at-yahoo.com>写在

新闻：#w ************** @ TK2MSFTNGP10.phx.gbl：

Date is a value type and value types cannot be null. Think of another way
to identify if the d variable has been given a specific value.
"John A Grandy" <johnagrandy-at-yahoo.com> wrote in
news:#w**************@TK2MSFTNGP10.phx.gbl:

显然是参考类型日期不能假设值Nothing，
因为以下代码失败：

Dim d As Date
......其他代码......
如果d什么都没有那么

结束如果

那么对于类型为Date的引用，Nothing的等价是什么？

apparently references of type Date can not assume the value Nothing,
because the following code fails:

Dim d As Date
......other code......
If d Is Nothing Then

End If

so then what is the equivalent to Nothing for a reference of type Date
?

*" John A Grandy" < johnagrandy-at-yahoo.com> scripsit：

* "John A Grandy" <johnagrandy-at-yahoo.com> scripsit:

显然，Date类型的引用不能假设值为Nothing，因为以下代码失败：

Dim d As Date
.. ....其他代码......
如果d什么都没有那么

结束如果

那么什么相当于没什么可供参考类型日期？

apparently references of type Date can not assume the value Nothing, because
the following code fails:

Dim d As Date
......other code......
If d Is Nothing Then

End If

so then what is the equivalent to Nothing for a reference of type Date ?

''DateTime''是一个所谓的值类型，而不是像

类这样的引用类型。


-

Herfried K. Wagner

MVP·VB Classic，VB.NET

< http://www.mvps.org/dotnet>

''DateTime'' is a so called "value type", not a reference type like
classes are.

--
Herfried K. Wagner
MVP · VB Classic, VB.NET
<http://www.mvps.org/dotnet>

John，

正如其他人指出的那样Date是一个值类型，你从来没有真正有一个日期的

引用。除非您将日期值包装起来，将

日期放在对象参考中，但这是另一回事...


但是你可以检查是否d = Date.MinValue以查看日期是否已将
设置为某个值。

John,
As the other have pointed out Date is a value type, you never really have a
reference to a Date. Unless of course you box the date value, by placing the
date in an object reference, that however is a different matter...

You can however check to see if d = Date.MinValue to see if the date has
been set to a value yet or not.

Dim d As Date
......其他代码......
如果d = Date.MinValue那么


希望这有帮助

周杰伦


John A Grandy < johnagrandy-at-yahoo.com>在消息中写道

新闻：％2 **************** @ TK2MSFTNGP10.phx.gbl ...显然类型为Date的引用不能假定值没什么，
，因为下面的代码失败了：

Dim d As Date
......其他代码......
如果d is Nothing然后

结束如果

那么对于Date类型的引用，什么是Nothing呢？

Dim d As Date
......other code......
If d = Date.MinValue Then
Hope this helps
Jay

"John A Grandy" <johnagrandy-at-yahoo.com> wrote in message
news:%2****************@TK2MSFTNGP10.phx.gbl... apparently references of type Date can not assume the value Nothing, because the following code fails:

Dim d As Date
......other code......
If d Is Nothing Then

End If

so then what is the equivalent to Nothing for a reference of type Date ?

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