处理下拉列表中的空值 [英] Handle Nulls in Dropdown Lists

问题描述

我的代码中显然存在nulls或其他问题。代码是：

I apparently have an issue with nulls, or something else, in my code. The code is:

代码开始

asp：DropDownList ID =" ddlCity" RUNAT = QUOT;服务器"的DataSourceID = QUOT; dsPatientDemosCity" DataTextField = QUOT;城市" DataValueField = QUOT;城市" SelectedValue ='<％＃Bind（" City"）％>'>

asp:DropDownList ID="ddlCity" runat="server" DataSourceID="dsPatientDemosCity" DataTextField="City" DataValueField="City" SelectedValue='<%# Bind("City") %>'>

END OF CODE

我收到以下错误：

'ddlCity'有一个SelectedValue无效，因为它在项目列表中不存在。

参数名称：值

'ddlCity' has a SelectedValue which is invalid because it does not exist in the list of items.
Parameter name: value

如何解决这个问题？

谢谢。

推荐答案

你有一个名为
City 的变量，它将保留所选的值？

Do you have a variable called City which will hold the selected value?

尝试在forums.asp.net上询问，其中有一些观众熟悉这些问题。例如，检查为初始状态添加
AppendDataBoundItems 属性和特殊列表项（"请选择"）的解决方案：
https://forums.asp.net/t/1056921.aspx 。

Try asking at forums.asp.net, which has an audience familiar with such problems. For example, check a solution that adds the AppendDataBoundItems attribute and a special list item ("Please select") for initial state: https://forums.asp.net/t/1056921.aspx.

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