Question

How do I go about getting the selected value from the DropDownList in asp.Net using selectedIndexChanged with an update Panel? I’ve tried but when I add the AutoPostBack to my DropDownList, it sends me to an error page saying it cannot find the resource.(doesn’t even hit my “selected_IndexChanged”) I have the hiddenField being assigned the selected value.

Here is my DropDownList:

<asp:ScriptManager ID="ScriptManager1" runat="server" />
    <asp:UpdatePanel runat="server" ID="UpdatePanel1">
        <ContentTemplate>
            <asp:DropDownList runat="server" ID="ddlCaseFilesNew" DataSourceID="dsCaseFiles"
                DataTextField="Display" DataValueField="FileID" OnPreRender="ddl_PreRender" Width="300px"
                AutoPostBack="true" OnSelectedIndexChanged="ddlCaseFilesNew_SelectedIndexChanged" Visible="False">
                <asp:ListItem>Item 1</asp:ListItem>
            </asp:DropDownList>
        </ContentTemplate>
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="ddlCaseFilesNew" EventName="SelectedIndexChanged" />
        </Triggers>
    </asp:UpdatePanel>

When I click on a value inside the DropDownList it sends me to a “cannot find resource” page. I have no idea why. It doesn’t even touch my “onSelectedIndexChanged”

  <script runat="server">
    protected void ddlCaseFilesNew_SelectedIndexChanged(object sender, EventArgs e)
    {
        hidNewCaseFile.Value = ddlCaseFilesNew.SelectedItem.Value;
    }
</script>

Answer 1

In your SelectedIndex function, use

string sValue = ((DropDownList)sender).SelectedValue;

Since it’s in an update panel, you likely won’t have access to it via the designer (this.DdlId).

Based on your comment in the OP, this is likely what you need:

protected void ddlCaseFilesNew_SelectedIndexChanged(object sender, EventArgs e)
{
    hidNewCaseFile.Value = ((DropDownList)sender).SelectedValue;
}

You also need to move your hidden field into the ContentTemplate.