How I Do Get Value From A Dropdownlist And Put In To A Label?

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C++

ASP.NET

ListView

DropDownList

Hello everybody

I'm trying to make a website on ASP.NET (VS2013 Express), in this website users can insert data to a MSSQL DB.

I'm using Insert Item Template from ListView, but i'm trying to reduce user mistakes introducing dropdownlist (it's a relational DB). I can make Cascading Dropdownlist but for some strange reason property SelectedValue=<%# Bind("Field1") %> does not work for me.

I Googled about and i find a way taking the Selected Value (with Autopostback enabled) and moving data into a label with Text =<%# Bind("Field1") %>

<asp:ListView ID="ListView1" runat="server" DataKeyNames="sequence" DataSourceID="Table3ID" GroupItemCount="3" InsertItemPosition="FirstItem">
            <InsertItemTemplate>
                <td  runat="server" style="">
                    Folio:
                    <asp:Label ID="Label2" runat="server" Text='<%# Bind("Folio") %>' Visible="False"></asp:Label>
                    <asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="True" DataSourceID="Folio" DataTextField="Folio" DataValueField="Folio">
                    </asp:DropDownList>
                    <asp:SqlDataSource ID="Folio" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString1 %>" 
                        SelectCommand="SELECT * FROM Table2">
                    </asp:SqlDataSource>
                    <br />Asignado:
                    <asp:Label ID="Label1" runat="server" Text='<%# Bind("Asignado") %>' Visible="True"></asp:Label>
                    <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" DataSourceID="Asignado" DataTextField="Nombre" DataValueField="sequence" >
                    </asp:DropDownList>
                    <asp:SqlDataSource ID="Asignado" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString1 %>" 
                        SelectCommand="SELECT * FROM Table1">
                    </asp:SqlDataSource>
                    <br />

and some behind code to enable javascript

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            ClientScript.RegisterStartupScript(GetType(),"obtieneAsignado","ddl1();", true);
        }
        protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
        {
            ClientScript.RegisterStartupScript(GetType(), "obtieneFolio", "ddl2();", true);
        }

And some JavaScript code

<script type="text/javascript">
    function ddl1() {
        document.getelementbyid('<%=ListView1.FindControl("Label1").ClientID%>').Value = document.getelementbyID('<%=ListView1.FindControl("DropDownList1").ClientID%>').SelectedValue;
    }
    function ddl2() {
        document.getelementbyid('<%=ListView1.FindControl("Label2").ClientID%>').Value = document.getelementbyID('<%=ListView1.FindControl("DropDownList2").ClientID%>').SelectedValue;
        if (<%=ListView1.FindControl("DropDownList2").ClientID%> == null || '<%=ListView1.FindControl("DropDownList1").ClientID%>' == null) return;
    }
</script>

Well, really it's a kind of Frankenstein solution cause i take pieces of code from lots of sites. The trouble here is no matter the way i take, i can't make the insert works. Apparently the Javascript doesn't work because the objects not exist, i get the error:

Object reference not set to an instance of an object.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Code Error: 


Línea 9:      <script type="text/javascript">
Línea 10:         function ddl1() {
Línea 11:             document.getelementbyid('<%=ListView1.FindControl("Label1").ClientID%>').Value = document.getelementbyID('<%=ListView1.FindControl("DropDownList1").ClientID%>').SelectedValue;
Línea 12:         }
Línea 13:         function ddl2() {

I appreciate your help