c# - Set Item limit to be display in ajaxToolkit ComboBox or set the Combobox position downwards in asp.net -

i have ajaxtoolkit combobox inside gridview , works perfectly, problem when click dropdown button list overlaps page want limit number displayed 10 items per scroll. next problem when try add update panel page, destroys rendering of combobox. how can solve this? in advance

here code combobox inside gridview

      <asp:gridview cssclass="pad" id="dgvorder" runat="server" borderstyle="double" autogeneratecolumns="false" onrowdatabound="dgvorder_rowdatabound" onrowdeleting="dgvorder_rowdeleting" horizontalalign="center" >         <columns>         <asp:templatefield headertext="no." accessibleheadertext="no.">                     <itemtemplate>                         <%# container.dataitemindex + 1 %>                     </itemtemplate>                 </asp:templatefield>             <asp:templatefield headertext ="description" accessibleheadertext="description">                            <itemtemplate >                             <ajaxtoolkit:combobox id="ddlitems" autopostback="true" appenddatabounditems="true" onmouseover="this.size=4;" onmouseout="this.size=1;" datatextfield="item_desc" datavaluefield="item_id"  runat="server" autocompletemode="suggest" iteminsertlocation="prepend" onselectedindexchanged="ddlitems_selectedindexchanged" dropdownstyle="dropdown" borderstyle="double" ></ajaxtoolkit:combobox> <br />                              <asp:requiredfieldvalidator id="requiredfieldvalidator2" runat="server" errormessage="please pick item" controltovalidate="ddlitems"></asp:requiredfieldvalidator>                             </itemtemplate>                            </asp:templatefield>             <asp:templatefield accessibleheadertext="inventory code" headertext="inventory code">                 <itemtemplate>                  <asp:label id="lblinvcode" runat="server" text=""></asp:label>                     </itemtemplate>             </asp:templatefield>             <asp:templatefield accessibleheadertext="qty" headertext="qty">                 <itemtemplate>              <asp:textbox id="txtqty" runat="server" ontextchanged="txtqty_textchanged" autopostback="true" onkeyup ="validatetext(this);"></asp:textbox><br />                     <asp:requiredfieldvalidator id="requiredfieldvalidator23" runat="server" errormessage="please input qty" controltovalidate="txtqty"></asp:requiredfieldvalidator>                  </itemtemplate>             </asp:templatefield>              <asp:templatefield accessibleheadertext="uom" headertext="uom">                 <itemtemplate>                     <asp:label id="lbluom" runat="server" text=""></asp:label>                     </itemtemplate>             </asp:templatefield>              <asp:templatefield accessibleheadertext="soq" headertext="soq">                 <itemtemplate>                     <asp:label id="lblsoq" runat="server" text=""></asp:label>                     </itemtemplate>             </asp:templatefield>               <asp:templatefield accessibleheadertext="reason" headertext="reason">                 <itemtemplate>                     <asp:textbox id="txtreason" runat="server" enabled="false"></asp:textbox>                     </itemtemplate>             </asp:templatefield>             <asp:commandfield showdeletebutton="true" />              </columns>     </asp:gridview>  

and here code updatepanel

<asp:updatepanel id="updatepanel1" runat="server">     <contenttemplate>  </contenttemplate>     <triggers>   (whole page inside)     <asp:asyncpostbacktrigger controlid="btnsearch" eventname="click" />     <asp:asyncpostbacktrigger controlid="txtidno" eventname="textchanged" />     </triggers>     </asp:updatepanel> 

long item lists / multiple input controls

all of items in combobox's list rendered web page exists in. autocompleteextender, on other hand, retrieves items servicemethod after page rendered. when combobox contains rather long list of items, or when have relatively large number of comboboxes on same page (or within same updatepanel), load times slowed down significantly. when comboboxes perform because of amount of markup must render browser, autocompleteextender can used instead increase performance.

<ajaxtoolkit:combobox id="combobox1" runat="server"  dropdownstyle="dropdown"  autocompletemode="none" casesensitive="false" rendermode="inline" iteminsertlocation="append" listitemhovercssclass="comboboxlistitemhover"   <asp:listitem>...</asp:listiem>   ... 

for more information can in link.