How to add dynamic AJAX ModalPopupExtender Modal Popup to ASP.Net Page

Hi i have created a class as follows which will create a dynamic popup

public static void createModal()
        {
            Button btnShow = new Button();
            btnShow.ID = "btnCancel";
            Panel p = new Panel();
            p.ID = "ModalPanel";
            p.Height = Unit.Percentage(300);
            p.Width = Unit.Percentage(800);

           Button btnCancel = new Button();
            btnCancel.Text = "Close";
            btnCancel.ID = "btnCancel";
            Page page = HttpContext.Current.CurrentHandler as Page;
            AjaxControlToolkit.ModalPopupExtender modalPop = new AjaxControlToolkit.ModalPopupExtender();

            modalPop.ID = "popUp";

            modalPop.PopupControlID = p.ID;

            modalPop.TargetControlID = btnShow.ID;

            modalPop.DropShadow = true;

            modalPop.CancelControlID = btnCancel.ID;
            //page.Form.Controls.Add(p);
            page.Form.Controls.Add(btnCancel);
            page.Form.Controls.Add(modalPop);
        }

And in my page my design is as follows

 <asp:ScriptManager ID="script" runat="server"></asp:ScriptManager>
            <asp:UpdatePanel ID="up" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="true">
<%--<Triggers>
                    <asp:PostBackTrigger ControlID="btnShow" />
                </Triggers>--%>                <ContentTemplate>
                    <asp:Button ID="btnShow" runat="server" Text="Open" OnClick="btnShow_Click"></asp:Button>
                </ContentTemplate>
            </asp:UpdatePanel>

This is my code on button click to show the popup

 protected void btnShow_Click(object sender, EventArgs e)
        {
            common.createModal(btnShow);
        }

If i didnot include the trigger on the page modal is not showing, but if I include the trigger modal popup is showing, can this be achieved with out registering the triggers