c# - ajax dropdown extender at runtime -

i've got textbox ajax dropdown extender. how make image 2 @ runtime , not when hovering on textbox. textbox "downbutton" should image 2 @ design time

how do or reading material on how this?

edit

all i've done far i'm trying first display correctly, otherwise have find way:

    <asp:content id="bodycontent" runat="server" contentplaceholderid="maincontent"> <asp:scriptmanager id="scriptmanager1" runat="server">             </asp:scriptmanager>     <div>         <asp:textbox id="txtresidence" runat="server"></asp:textbox>        <asp:dropdownextender id="txtresidence_dropdownextender" runat="server"             dynamicservicepath="" enabled="true" targetcontrolid="txtresidence"            dropdowncontrolid="pnlres">        </asp:dropdownextender>     </div>    <div>          <asp:panel id="pnlres" runat="server">         <asp:treeview id="residencetreeview" runat="server" showlines="true" populatenodesfromclient="false" backcolor="#99ccff" style="width:100%" showexpandcollapse="false">             <nodes>                 <asp:treenode text="1" value="1">                     <asp:treenode text="1.1" value="1.1"></asp:treenode>                     <asp:treenode text="1.2" value="1.2"></asp:treenode>                 </asp:treenode>                 <asp:treenode text="2" value="2">                     <asp:treenode text="2.1" value="2.1"></asp:treenode>                     <asp:treenode text="2.2" value="2.2"></asp:treenode>                 </asp:treenode>             </nodes>         </asp:treeview>         </asp:panel>    </div> </asp:content> 

try adding script.

 <script type="text/javascript">    function pageload() {       $find('txtresidence_txtresidence_dropdownextender')._dropwrapperhoverbehavior_onhover();   $find('txtresidence_txtresidence_dropdownextender').unhover = visibleme; }  function visibleme() {     $find('txtresidence_txtresidence_dropdownextender')._dropwrapperhoverbehavior_onhover(); }