I'm just starting in Asp.Net .

A page have a ListBox and I want that on the OnSelectedIndexChanged
event a second page be called passing the value of the selected
option. I want the second page to show its own url.

This is the aspx of the first page:

   <form id="form1" runat="server">
   <div>
       <asp:ListBox ID="ListBox1" runat="server" AutoPostBack="true"
           OnSelectedIndexChanged="ListBox1_SelectedIndexChanged">
           <asp:ListItem Value="1" Text="1st Option" />
           <asp:ListItem Value="2" Text="2nd Option" />
           <asp:ListItem Value="3" Text="3rd Option" />
       </asp:ListBox>
   </div>
   </form>

The problem is that the ListBox control does not have a PostBackUrl
event like the Button control has and I don't want to force the user
to choose an option and then click a button. I want it to happen at
the OnSelectedIndexChanged event and be able to use PreviousPage in
the second page. I know there are other controls that can use the
PostBackUrl event and could be used in this simple case but the number
of options can be tens or hundreds to be filled from a database and I
want it to render a select tag.

The only solution I see is to use Response.Redirect:

   protected void ListBox1_SelectedIndexChanged(object sender,
EventArgs e)
   {
       Response.Redirect("secondPage.aspx?option=" +
ListBox1.SelectedValue);
   }

Using the redirect adds one more round trip. Beyond that what to do if
I needed to post it in instead of passing the pairs in a query
string?

I tried to change the action attribute of the form to
"secondPage.aspx" but asp.net always render it as "default.aspx".

What is the most used pattern here?

Regards, Clodoaldo Pinto Neto