how to open a popup when click anywhere in gridview row without postback in codebehind

<asp:UpdatePanel ID="UpdatePanel3" runat="server">

            <ContentTemplate>
                <asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False" ShowFooter="True"
                    OnPageIndexChanging="GridView1_PageIndexChanging" Style="table-layout: fixed;"
                    CssClass="mGrid" DataKeyNames="AreaID" PagerStyle-CssClass="pgr" ShowHeader="False"
                    AlternatingRowStyle-CssClass="alt" Width="652px" Height="625px" OnRowDataBound="GridView1_RowDataBound"
                    OnSelectedIndexChanged="GridView1_SelectedIndexChanged">
                    <%-- <BoundaryStyle BorderColor="Gray" BorderStyle="Solid" BorderWidth="1px" />--%>
                    <AlternatingRowStyle CssClass="alt" />
                    <Columns>
                        <asp:TemplateField ItemStyle-Width="43px">
                            <ItemTemplate>
                                <%#Container.DataItemIndex+1 %>
                            </ItemTemplate>
                            <ItemStyle Width="43px" />
                        </asp:TemplateField>
                        <asp:BoundField HeaderText="ID" DataField="AreaID" HeaderStyle-HorizontalAlign="Left"
                            Visible="false">
                            <HeaderStyle HorizontalAlign="Left" />
                        </asp:BoundField>
                        <asp:TemplateField ShowHeader="False">
                            <ItemTemplate>
                                <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="false" CommandName=""
                                    Text='<%# Eval("Area") %>'></asp:LinkButton>
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
                    <PagerStyle Font-Names="Calibri" Font-Size="12px" Width="303px" BackColor="#000000"
                        HorizontalAlign="Center" ForeColor="White" />
                </asp:GridView>


                   <asp:Button ID="btnTest"  runat="server"  onclick="gridview_click" />
            </ContentTemplate>
        </asp:UpdatePanel>

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
  {
     if (e.Row.RowType == DataControlRowType.DataRow)
          {
              e.Row.Attributes.Add("onmouseover", "this.style.backgroundColor='#ceedfc'");
              e.Row.Attributes.Add("onmouseout", "this.style.backgroundColor=''");
              e.Row.Attributes.Add("style", "cursor:pointer;");
              //e.Row.Attributes.Add("onclick", "location='patron_detail.aspx?id=" + e.Row.Cells[0].Text + "'");
              e.Row.Attributes["OnClick"] = Page.ClientScript.GetPostBackClientHyperlink(btnTest, , e.Row.RowIndex.ToString());
          }

      }

 protected void GridView1_OnClick(object sender, EventArgs e){

       //{
       btnNew.Visible = false;
       btnUpdate.Visible = true;
       this.ModalPopupExtender1.Show();

   }

        public class btnTest : Button, IPostBackEventHandler
   {

       // Use the constructor to defined default label text.
       public btnTest()
       {
       }

       // Implement the RaisePostBackEvent method from the
       // IPostBackEventHandler interface.
       public void RaisePostBackEvent(string eventArgument)
       {
           //You receive the row number here.
       }
   }