如何在asp.net C＃Web窗体应用程序中基于下拉列表的选定值填充文本框？

Question

I have a dropdown list (doc_rvw_sub_recip_list) that is populated with names from tbl_ad_users. tbl_ad_users contains a field titled "domain_user". I would like to populate an asp:hiddenfield (hdn_domain_user) with the "domain_user" based on the selected value in the doc_rvw_sub_recip_list dropdown list. For testing I used a dropdown list (domain_user_ddl) instead of a hidden field, and it works as needed. But I don't know how to get the value into a hidden field as opposed to using a dropdown list.

The following is doc_rvw_sub_recip_list:

<asp:DropDownList ID="doc_rvw_sub_recip_list" runat="server" DataSourceID="sdc_ad_user_list" DataTextField="name" DataValueField="email_address" AppendDataBoundItems="true" AutoPostBack="true"><asp:ListItem Value="">Please Select</asp:ListItem></asp:DropDownList>

The following is the sql data source for domain_user_ddl:

<asp:SqlDataSource ID="sdc_domain_user_ddl" runat="server" ConnectionString='<%$ ConnectionStrings:idrfConnectionString %>' SelectCommand="SELECT [domain_user] FROM [tbl_ad_users] WHERE ([email_address] = @email_address)">
            <SelectParameters>
                <asp:ControlParameter ControlID="doc_rvw_sub_recip_list" PropertyName="SelectedValue" Name="email_address" Type="String"></asp:ControlParameter>
            </SelectParameters>
        </asp:SqlDataSource>

The following is domain_user_ddl:

<asp:DropDownList ID="domain_user_ddl" runat="server" DataSourceID="sdc_domain_user_ddl" DataTextField="domain_user" DataValueField="domain_user" AutoPostBack="true"></asp:DropDownList>

How do I get this to work for hdn_domain_user just as it works for domain_user_ddl?

Answer 1

ASPX

Add a OnSelectedIndexChanged event to your dropdown...

<asp:DropDownList ID="doc_rvw_sub_recip_list" runat="server" DataSourceID="sdc_ad_user_list" DataTextField="name" DataValueField="email_address" AppendDataBoundItems="true" AutoPostBack="true" OnSelectedIndexChanged="doc_rvw_sub_recip_list_SelectedIndexChanged"><asp:ListItem Value="">Please Select</asp:ListItem></asp:DropDownList>

Add your hidden field...

<asp:HiddenField runat="server" ID="hdn_domain_user" />

Code Behind

Handle the SelectedIndexChanged event...

protected void doc_rvw_sub_recip_list_SelectedIndexChanged(Object sender, EventArgs e)
{
    // Populate the hidden field if the dropdown has a selected value
    if (doc_rvw_sub_recip_list.SelectedValue != null)
        hdn_domain_user.Value = doc_rvw_sub_recip_list.SelectedValue;
}