DropDownList“具有无效的SelectedValue，因为它不存在于项列表” [英] DropDownList "has a SelectedValue which is invalid because it does not exist in the list of items"

问题描述

我有一个ASP.NET DropDownList，我将数据绑定到一个对象列表，然后它抛出一个异常。这个错误让我很坚强，因为消息是错误的，清单中的值存在于项目列表中，如屏幕截图所示：

以下是相关的ASP.NET标记：

 < asp：DropDownList ID =_ ddlRequestsrunat =serverAppendDataBoundItems =trueDataTextField =RequestNumberDataValueField =RequestNumber> ; 
< asp：ListItem Text =Value =/> 
< / asp：DropDownList> 
  

解决方案

这可能值得首先进行数据绑定，然后添加您的空白值。以下行：

  _ddlRequest.Datasource = request; 
 _ddlRequest.DataBind（）; 
 _ddlRequest.Insert（0，new ListItem（，））; 
  

我建议这样做的唯一原因是我在遇到挫折之前和之后遇到这个问题一段时间刚刚解决了这样做。

I have a ASP.NET DropDownList, which I data-bind to a list of objects, and then it throws an exception. This error is driving me nuts, because the message is wrong, and the value clearly does exist in the list of items, as shown by the screenshot:

Here's the relevant ASP.NET markup:

<asp:DropDownList ID="_ddlRequests" runat="server" AppendDataBoundItems="true" DataTextField="RequestNumber" DataValueField="RequestNumber">
    <asp:ListItem Text="" Value="" />
</asp:DropDownList>

解决方案

It may be worth first databinding and then adding your blank value. Something along the lines of:

_ddlRequest.Datasource = request;
_ddlRequest.DataBind();
_ddlRequest.Insert(0, new ListItem("", ""));

The only reason I suggest this is that I came across this before and after banging my head in frustration for a while just settled on doing it this way instead.

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