ajaxToolkit:ModalPopupExtender raise event on being shown ..

Question

Hi all,

i am using ajaxToolkit:ModalPopupExtender and want to raise a server side event on its visibility...

<script language="javascript" type="text/javascript">
    function pageLoad() {
             $find('modalpopup').show();
    }
</script>
--------------
<ajaxToolkit:ModalPopupExtender ID="modalpopup" runat="server"
    TargetControlID="dummyLink"
    PopupControlID="EditorPanel"
    BackgroundCssClass="modalBackground" 
    DropShadow="true" 
    BehaviourID="modalpopup"> 
</ajaxToolkit:ModalPopupExtender>

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now what should i do to raise a server side event through ModalPopupExtender control ?

Note : (Modalextender doesn't have any button or control so server side event should be raised automatically on its visiblity)