我如何...如何最好地在Windows窗体应用程序中指出存在“无价值”的情况。在日期字段？

问题描述：

Visual Studio -Visual Basic - Windows窗体。

与Sql server（10.50）dbase的ODBC连接。

数据库日期Cloumn

一般设置

- 数据类型=日期。

- 允许Nulls =是。

如何最好地在Windows窗体中指出日期字段中有无价值？

我应该编码清除（设置为空）数据库中的值吗？（如果Possbile）？

或

我应编码以呈现空值或defauot值为没有价值？

我的尝试：

我在我的窗口上的Datagridview中清除了日期，并将1900-01-01保存到数据库日期cloumn。

不确定这是应用程序，ODBC连接还是提供此服务器的服务器？

另外

Datetimepicker：如果为null，如何在Windows窗体中指出日期字段中有无值。

Visual Studio -Visual Basic - Windows Form.
ODBC connection to Sql server(10.50) dbase.

Database date Cloumn
General settings
- Data type = date.
- Allow Nulls = Yes.

How best to indicate in the Windows Form that there is "No value" in the date field?

Should i code to clear( set to null ) the value in the database? (if Possbile)?

or

Should i code to present an Null value or defauot value as "No value" ?

What I have tried:

I have cleared dates in a Datagridview on my windows from and "1900-01-01" is saved to the database date cloumn.
Not sure if this is the App, ODBC conenction or the Server providing this ?

Also
Datetimepicker : if null , How best to indicate in the Windows Form that there is "No value" in the date field.

答

似乎你正在寻找 DBNull.Value [ ^ ]

Seems you're looking for DBNull.Value[^]

If DbNUll.Value.Equals(DataBaseValue) Then
    'set default value
End If

或：

or:

DataBaseValue = IIf(Not DbNUll.Value.Equals(DataBaseValue), DataBaseValue, New DateTime(1900, 1, 1))

注意： DataBaseValue 是要检查null的变量/字段。

Note: DataBaseValue is a variable/field you want to check for null.

您可以使用DateTimePicker.Checked属性（System.Windows.Forms）| Microsoft Docs [ ^ ]

除此之外，您可能必须从DateTimePicker派生控件并覆盖OnPaint以显示消息或类似内容。应该不难，但我自己不需要这样做。

You could use the DateTimePicker.Checked Property (System.Windows.Forms) | Microsoft Docs[^]
Other than that, you'd probably have to derive a control from the DateTimePicker and override OnPaint to display a message or similar. Shouldn't be difficult, but I haven't needed to do it myself.

我如何...如何最好地在Windows窗体应用程序中指出存在“无价值”的情况。在日期字段？

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