如何创建一个允许DBNull的ComboBox列表？

问题描述

如何为允许DBNull的ComboBox创建列表？

How to create a list for a ComboBox that allows DBNull?

我试过 int？但 int？ >与 DBNull 不同，并且组合框不使用null值。

I tried int? But int? is not the same as DBNull and the combobox does not work with the null value.

我的datagridview组合框需要 DBNull 。

My datagridview combobox, needs DBNull.

>

I did:

var machineComboList = this.eMDataSet1.Machines.Select(row => new
            {
                Key = (int?) row.MachineID,
                Value = row.Description
            }).ToList();

int? nullValue = DBNull.Value;
machineComboList.Add(new { Key = nullValue, Value = "All" });

我想把一个DBNull值放入Key。 int 不起作用。

I want to put a DBNull value into "Key". Using int? does not work.

相关：

推荐答案

DBNull 仅适用于ADO.NET，以区分缺失值和空值。

DBNull is only intended for ADO.NET, to make a distinction between a missing value and a null value.

int？可以是 null - 这可能是你要找的。它不能是 DBNull ，因为它们是不兼容的类型。

int? can be null -- this is probably what you're looking for. It can never be DBNull, as they are incompatible types.

很少能直接使用 DBNull 以外的ADO.NET调用。从数据库中读取时，通常会这样翻译：

It is rare to work directly with DBNull outside of ADO.NET calls. When reading from the database, you'll usually translate it like this:

object dbValue = ...;
int? intValue = dbValue != DBNull.Value ? (int)dbValue : (int?)null;

或者，如果你对返回的数据类型更加信任，你可以缩短到：

Or if you're a little more trusting of the data types returned, you can shorten it to this:

object dbValue = ...;
int? intValue = dbValue as int?;

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