asp.net - jQuery Dialog with internal asp:Button dont want it to close the dialog -

question: how stop asp:button lives inside aspx page displayed inside jquery dialog closing dialog. want keep dialog open , use info input form database table work with.

i have simple demo code behind adds 2 numbers (very crude , elementary) , when hit 'button' add numbers closes dialog box. adds numbers dialog box closes.

calling dialog:

 <script>         function showdialog() {             var mydiv = $("#dialog-form").dialog({                 modal: true,                 autoopen: false,                 height: 500,                 width: 500                             });             mydiv.load('effortsubmittalpage.aspx');             $("#dialog-form").parent().appendto($("form:first"));             mydiv.dialog('open');             return false;         }     </script> 

content page displays in dialog:

<asp:content id="headercontent" runat="server" contentplaceholderid="headercontent">     <asp:updatepanel id="wrapper" runat="server" updatemode="conditional">         <contenttemplate>             <table id="table1" cellspacing="1" cellpadding="1" width="300" border="0">                  <tr>                     <td>                         <asp:label id="label1" runat="server">first number:</asp:label>                     </td>                     <td>                         <asp:textbox id="txtfirstnumber" runat="server"></asp:textbox>                     </td>                 </tr>                 <tr>                     <td>                         <asp:label id="label2" runat="server">second number:</asp:label>                     </td>                     <td>                         <asp:textbox id="txtsecondnumber" runat="server"></asp:textbox>                     </td>                 </tr>                 <tr>                     <td>                         <asp:label id="label3" runat="server">sum:</asp:label>                     </td>                     <td>                         <asp:textbox id="txtsum" runat="server"></asp:textbox>                     </td>                 </tr>                 <tr>                     <td>                         <asp:button id="button1"                             runat="server"                             text="add numbers"                             onclick="button1_click"></asp:button>                     </td>                     <td></td>                 </tr>             </table>          </contenttemplate>     </asp:updatepanel> </asp:content> 

content code behind

protected void button1_click(object sender, eventargs e)         {             var inttotal = 0;             var intfirstnumber = 0;             var intsecondnumber = 0;              intfirstnumber = int.parse(txtfirstnumber.text);             intsecondnumber = int.parse(txtsecondnumber.text);              inttotal = intfirstnumber + intsecondnumber;             txtsum.text = inttotal.tostring();         }     } 

any advice welcome..
andy.