如何修复“'ddlAssignedTo' 有一个无效的 SelectedValue，因为它不存在于项目列表中

我加载网格视图，网格视图有一个编辑和删除按钮。

我点击“编辑”，然后我得到：“ddlAssignedTo' has a SelectedValue which is invalid because it does not exist in the list of items. Parameter name: value

我知道我收到此错误是因为ddlAssignedTo为 null - ddlAssignedTo 的数据库中不存在任何内容。

我想做的就是更新当前值。

所以，我的问题是，如果当前值为空，如何为 ddlAssignedTo 分配默认值，以便如果数据库中当前不存在值，则以默认值为准？

这是一些代码：

Markup:

<asp:TemplateField HeaderText="Assigned To">
    <EditItemTemplate>
      <asp:DropDownList ID="ddlAssignedTo" runat="server" 
                        DataSourceID="SubjectDataSource"
                        DataTextField="fullname" DataValueField="empl_Id"
                        SelectedValue='<%# Bind("AssignedTo") %>'>
        <asp:ListItem Value="">--Select Name--</asp:ListItem>
      </asp:DropDownList>
    </EditItemTemplate>
    <ItemTemplate>
        <asp:Label ID="lblAssigned" runat="server" 
                   Text='<% #Bind("fullname") %>'></asp:Label>
    </ItemTemplate>
</asp:TemplateField

<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
                   ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
                   SelectCommand="SELECT Distinct [rownum],[reqnum], AssignedTo, (empl_first + ' ' + empl_last) fullname, [reqrecdate], [reqrecfrom], [skillsets], [application], [hoursperweek], [fromdate], [todate], [status], [statusupdate], [statusupby] FROM [requestinfo] left join employee on requestInfo.AssignedTo=employee.empl_id ORDER BY [reqnum]" 
                   UpdateCommand="INSERT INTO [requestinfo] ([reqnum], [reqrecdate], [reqrecfrom], [skillsets], [application], [hoursperweek], [fromdate], [todate], [status], [statusupdate], [statusupby],[AssignedTo]) VALUES (@reqnum, @reqrecdate, @reqrecfrom, @skillsets, @application, @hoursperweek, @fromdate, @todate, @status, @statusupdate, @statusupby,@empl_id)">
    <DeleteParameters>
        <asp:Parameter Name="rownum" Type="Int32" />
    </DeleteParameters>
    <UpdateParameters>
        <asp:Parameter Name="reqnum" Type="String" />
        <asp:Parameter DbType="DateTime" Name="reqrecdate" />
        <asp:Parameter Name="reqrecfrom" Type="String" />
        <asp:Parameter Name="skillsets" Type="String" />
        <asp:Parameter Name="application" Type="String" />
        <asp:Parameter Name="hoursperweek" Type="Int32" />
        <asp:Parameter DbType="DateTime" Name="fromdate" />
        <asp:Parameter DbType="DateTime" Name="todate" />
        <asp:Parameter Name="status" Type="String" />
        <asp:Parameter DbType="DateTime" Name="statusupdate" />
        <asp:Parameter Name="statusupby" Type="String" />
        <asp:Parameter Name="empl_id" Type="String" />
        <asp:Parameter Name="rownum" Type="Int32" />
    </UpdateParameters>
</asp:SqlDataSource>
<asp:SqlDataSource ID="SubjectDataSource" runat="server" 
                   ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
                   SelectCommand="SELECT empl_id,  (empl_first + ' ' + empl_last) fullname FROM dbo.Employee order by empl_last">
</asp:SqlDataSource>

隐藏代码：

Protected Sub GridView1_RowUpdating(ByVal sender As Object, ByVal e As GridViewUpdateEventArgs) Handles GridView1.RowUpdating

    Dim dd As DropDownList = DirectCast(GridView1.Rows(e.RowIndex).FindControl("ddlstatus"), DropDownList)
    e.NewValues("status") = dd.SelectedItem.Text
    Dim ddAssigned As DropDownList = DirectCast(GridView1.Rows(e.RowIndex).FindControl("ddlAssignedTo"), DropDownList)

    If String.IsNullOrEmpty(ddAssigned.SelectedValue) Then
        ddAssigned.SelectedValue = "shhhh"
    Else
        e.NewValues("empl_id") = ddAssigned.SelectedValue
    End If

    SqlDataSource1.DataBind()
End Sub

看看问题中@cosmin.onea提供的解决方案“DropDownList1”的 SelectedValue 无效，因为它不存在于项目列表中

该解决方案设置AppendDataBoundItems="true" on the DropDownList并创建一个nullableListItem 以便您的DropDownList即使表中的字段为空也会绑定。

应用于OP的问题时，以下代码片段将提供一个选项，当AssignedTo字段为空时将选择该选项。

<asp:DropDownList ID="ddlAssignedTo" runat="server" 
    DataSourceID="SubjectDataSource" 
    DataTextField="fullname" DataValueField="empl_Id" 
    SelectedValue='<%# Bind("AssignedTo") %>' 
    AppendDataBoundItems="true">
        <asp:ListItem Text="Select" Value="" />
</asp:DropDownList>