Gridview Select/Buttonfield event to get a dropdownlist value and goto URL containing dropdown text

I have a Gridview, with a template field of a dropdown like this
 <asp:TemplateField>                     <ItemTemplate>                         <asp:DropDownList runat="server" ID="DD1">                         <asp:ListItem Value="P1">Page1</asp:ListItem>                         <asp:ListItem Value="P2">Page2</asp:ListItem>                    ...