将null值传递给DateTime属性 [英] Passing a null value to a DateTime property

问题描述

我有一个包含多个属性的类，其中一个属于DateTime

数据类型。但是，这个属性并不总是有价值，我需要

稍后检查它是否有值。


当我创建一个新的该类的实例，此属性获取{1/1/1}的默认值

，我根本不需要，因为这是完全有效的

date。


有没有办法让DateTime数据类型根本没有值，

我可以稍后查看？


或者是不使用DataTime数据类型并使用通用对象

数据类型的答案？


感谢任何帮助。


Mark

Hi,

I have a class with several properties, one of which is of the DateTime
datatype. However, this property will not always have a value, and I need to
check later whether it has a value or not.

When I create a new instance of the class, this property acquires a default
value of {1/1/1}, which I don''t want at all, as that is a perfectly valid
date.

Is there any way to cause a DateTime datatype to have no value at all, which
I can check later?

Or is the answer not to use a DataTime datatype and use a generic object
datatype instead?

Any assistance gratefully received.

Mark

推荐答案

日期是值类型，而不是引用类型，因此它们不能为null ，他们

始终保持一个价值。你可以使用DateTime.MinValue作为特殊值吗

表示没有值？


-


Best问候，


Carlos J. Quintero


MZ-Tools：Visual Studio .NET，VB6，VB5和VBA的生产力加载项

您可以更快地编码，设计和记录。

加载项开发人员的免费资源：
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" Mark Rae" <毫安** @ mark-N-O-S-P-A-M-rae.co.uk> escribióenel mensaje

news：ev ************** @ TK2MSFTNGP14.phx.gbl ...

Dates are value types, not reference types, so they can not be null, they
hold always a value. Could you use DateTime.MinValue as a special value to
denote no value?

--

Best regards,

Carlos J. Quintero

MZ-Tools: Productivity add-ins for Visual Studio .NET, VB6, VB5 and VBA
You can code, design and document much faster.
Free resources for add-in developers:
http://www.mztools.com

"Mark Rae" <ma**@mark-N-O-S-P-A-M-rae.co.uk> escribió en el mensaje
news:ev**************@TK2MSFTNGP14.phx.gbl...

我有一个包含多个属性的类，其中一个是DateTime
数据类型。但是，此属性并不总是有值，我需要稍后检查它是否有值。

当我创建类的新实例时，此属性获取
默认值{1/1/1}，我根本不需要，因为这是一个完全有效的日期。

有什么办法吗？导致DateTime数据类型根本没有值，
我可以稍后检查？

或者是不使用DataTime数据类型并使用通用对象的答案
数据类型相反？

感激不尽的任何帮助。

Mark

Hi,

I have a class with several properties, one of which is of the DateTime
datatype. However, this property will not always have a value, and I need
to check later whether it has a value or not.

When I create a new instance of the class, this property acquires a
default value of {1/1/1}, which I don''t want at all, as that is a
perfectly valid date.

Is there any way to cause a DateTime datatype to have no value at all,
which I can check later?

Or is the answer not to use a DataTime datatype and use a generic object
datatype instead?

Any assistance gratefully received.

Mark

Mark，


在.NET 2.0中，您将使用Nullable< T>，类型参数T

等于DateTime。这将生成一个具有HasValue

属性的结构，如果有值则为true，如果为null则为false。


如果您使用的是在2.0之前的.NET版本，然后你可以使用

SqlDateTime，它支持null语义。


希望这会有所帮助。

-

- Nicholas Paldino [.NET / C＃MVP]

- mv *@spam.guard.caspershouse.com


" Mark Rae" <毫安** @ mark-N-O-S-P-A-M-rae.co.uk>在消息中写道

news：ev ************** @ TK2MSFTNGP14.phx.gbl ...

Mark,

In .NET 2.0, you would use the Nullable<T>, with the type parameter T
equal to DateTime. This will produce a structure which has a HasValue
property which is true if there is a value, false if it is null.

If you are using a version of .NET before 2.0, then you could use the
SqlDateTime, which supports null semantics.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard.caspershouse.com

"Mark Rae" <ma**@mark-N-O-S-P-A-M-rae.co.uk> wrote in message
news:ev**************@TK2MSFTNGP14.phx.gbl...

我有一个包含多个属性的类，其中一个是DateTime
数据类型。但是，此属性并不总是有值，我需要稍后检查它是否有值。

当我创建类的新实例时，此属性获取
默认值{1/1/1}，我根本不需要，因为这是一个完全有效的日期。

有什么办法吗？导致DateTime数据类型根本没有值，
我可以稍后检查？

或者是不使用DataTime数据类型并使用通用对象的答案
数据类型相反？

感激不尽的任何帮助。

Mark

Hi,

I have a class with several properties, one of which is of the DateTime
datatype. However, this property will not always have a value, and I need
to check later whether it has a value or not.

When I create a new instance of the class, this property acquires a
default value of {1/1/1}, which I don''t want at all, as that is a
perfectly valid date.

Is there any way to cause a DateTime datatype to have no value at all,
which I can check later?

Or is the answer not to use a DataTime datatype and use a generic object
datatype instead?

Any assistance gratefully received.

Mark

" Carlos J. Quintero [ .NET MVP] < CA ***** @ NOSPAMsogecable.com>写在

消息新闻：OK ************** @ tk2msftngp13.phx.gbl ...

"Carlos J. Quintero [.NET MVP]" <ca*****@NOSPAMsogecable.com> wrote in
message news:OK**************@tk2msftngp13.phx.gbl...

可以你使用DateTime.MinValue作为特殊值来表示没有值？

Could you use DateTime.MinValue as a special value to denote no value?

可能 - 谢谢你的回答。

Possibly - thanks for the answer.

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