允许为空 [英] Allow Null

问题描述

我有一堆文本框，可以让它们为空


如何编程呢？我一直收到错误，说Null不再支持


Sandy

解决方案

" Sandy" <一个******* @ discussions.microsoft.com> schrieb

我有一堆文本框，它们可以是
null。

如何编程？我一直收到一个错误，说Null没有得到更长时间的支持。

你在谈论数据库中的Null值吗？它由

DBNull.Value表示。您无法将DBNull设置为文本框。一个文本框只包含

a字符串（长度0到

远远超过你可以读取和写入并且适合你的内存-without-swappi

ng-five-days-long）。我想说什么？...啊，好的：你/可以/使用

特殊字符串，比如（Null）表示文本框中的Null值，但仅当此特殊字符串永远不是

数据库中的正常字段内容时才会显示
。即使它不是非常用户友好，因为用户可以输入
来输入这个字符串来存储Null值。我可能会在文本框前面使用一个复选框

（没有文字）。如果选中，则文本框内容为

存储在数据库中，否则存储空值。

-

Armin


如何报价以及原因：
http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

嗨Armin


我想我不太清楚。这些文本框未连接到任何数据库。它们是可以包含DateTime值的文本框，或者不包含任何内容。我需要的代码基本上是如果文本框为空，请忽略与该文本框相关的代码。


生成的错误是：System.InvalidCastException。从字符串"中删除键入''Date''无效。


如果我发现文本框默认为00:00:00时间值，如果它们是空白的话，那就行了，但我不知道该怎么做


只要所有文本框都填充了一段时间，代码就可以了。如果有些空白，我会收到错误


任何想法


Sandy

< blockquote>嗨桑迪，


你的意思是

\\\

dim mydate as date

if isdate（textbox1.text）然后

mydate = cdate（textbox1.text）

结束如果

///

我希望这有帮助吗？


Cor

I have a bunch of textboxes that it is all right for them to be null

How do I program that? I keep getting an error that says Null is no longer supported

Sandy

解决方案

"Sandy" <an*******@discussions.microsoft.com> schrieb

I have a bunch of textboxes that it is all right for them to be
null.

How do I program that? I keep getting an error that says Null is no
longer supported.

You''re talking about the Null value in databases? It''s represented by
DBNull.Value. You can not set DBNull into a textbox. A textbox only contains
a string (length 0 to
much-more-than-you-can-read-and-write-and-fits-in-your-memory-without-swappi
ng-five-days-long). What did I wanna say?... Ah, ok: You /could/ use a
special string, like "(Null)" to represent a Null value in a textbox, but
only if this special string will never be a normal field content in the
database. Even if, it''s not very user friendly because the user would have
to type this string to store a Null value. I''d probably use a checkbox
(without text) in front of the textbox. If checked, the textbox'' content is
stored in the DB, otherwise Null is stored.
--
Armin

How to quote and why:
http://www.plig.net/nnq/nquote.html
http://www.netmeister.org/news/learn2quote.html

Hi Armin

I guess I wasn''t too clear. These textboxes are not connected to any database. They are textboxes that can contain a DateTime value or can contain nothing. I need code that essentially says "If the textbox is empty, disregard the code that pertains to that textbox."

The error generated is: "System.InvalidCastException. Cast from string "" to type ''Date'' is not valid.

If I could find away to have the textboxes default to a 00:00:00 time value if they were blank, that would work, but I don''t know how to do that

As long as all the textboxes are filled in with a time, the code works. If some are left blank, I get the error

Any ideas

Sandy

Hi Sandy,

You mean
\\\
dim mydate as date
if isdate(textbox1.text) then
mydate=cdate(textbox1.text)
end if
///
I hope this helps?

Cor

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