Prevent CascadingDropDown from making initial AJAX call

Question

I'm going to pre-populate my drop down lists on the server side. I only want the cascading drop-down to fire if the parent control changes.

Answer 1

Populate your parent ListBox from the code-behind, and set its "autopostback" attribute to true. Set OnSelectedIndexChanged="PopulateChildListBox"

Put the child ListBox in an UpdatePanel, and associate the parentListBox with the Updatepanel

    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="lbParent" />
        </Triggers>
        <ContentTemplate>
            <asp:ListBox ID="lbChild" runat="server" />
        </ContentTemplate>
    </asp:UpdatePanel>

In your code-behind, have the "PopulateChildListBox" method fill the child ListBox

protected void PopulateChildListBox(object sender, EventArgs e)
{
    // Get the data for the child listbox
    lbChildListBox.DataBind();
}

So, your child listbox only ever updates its content (via Asp.Net AJAX) when the parent ListBox changes.