<form id="form1" runat="server">
     <asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
     <div>
     <br />
     <asp:Label ID="LabelText" runat="server" Text="Wybierz element." Width="161px"></asp:Label>
     <asp:Panel ID="panelDropDown" runat="server" style="display:none; visibility:hidden;" CssClass="ContextMenuPanel">
           <asp:LinkButton ID="btnHp" runat="server" Text="HP" CssClass=" ContextMenuItem" OnClick=" OnItemSelect "></asp:LinkButton>
           <asp:LinkButton ID="btnCompaq" runat="server" Text="Compaq" CssClass="ContextMenuItem" OnClick=" OnItemSelect "></asp:LinkButton>
           <asp:LinkButton ID="btnDell" runat="server" Text="Dell" CssClass="ContextMenuItem" OnClick="OnItemSelect"></asp:LinkButton>
     </asp:Panel>
     <cc1:DropDownExtender ID="DropDownExtender1" runat="server" TargetControlID="LabelText" DropDownControlID="panelDropDown">
     </cc1:DropDownExtender>
     <br /><br /><br />
     <asp:UpdatePanel ID="UpdatePanel1" runat="server">
     <ContentTemplate>
          <asp:Label ID="lblSelectedValue" runat="server" Text=""></asp:Label>
     </ContentTemplate>
     <Triggers>
          <asp:AsyncPostBackTrigger ControlID="btnHp" EventName="Click" />
          <asp:AsyncPostBackTrigger ControlID="btnCompaq" EventName="Click" />
          <asp:AsyncPostBackTrigger ControlID="btnDell" EventName="Click" />
     </Triggers>
     </asp:UpdatePanel>
     </div>
</form>
