Bind the grid on modal page via clicking of link button in primary grid

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HTML

C#5.0

Here is my html code in which I am trying to bind the second grid on clicking of Link button in first grid.

<%@ Page Title="" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="CartList.aspx.cs" Inherits="Delta.WebForm3" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="server">

    <style type="text/css">
       .modalBackground 
        {
            background-color: Gray;
            filter:alpha(opacity=70);
            opacity:0.7; 
        } 

        .modalPopup 
        {
            background-color:#ffffdd; 
            border-width:3px; 
            border-style:solid; 
            border-color:Gray; 
            padding:3px; 
            width:250px; 
        }
    </style>

   

    <div class="row">
         <cc1:ToolkitScriptManager  runat="server">
        </cc1:ToolkitScriptManager>
        <div class="col-lg-12 col-md-12 col-xs-12">
            <asp:GridView ID="GridView1" runat="server" Width="100%" AutoGenerateColumns="False" 
            AllowSorting="true"  OnSorting="GridView1_Sorting" OnRowCommand="GridView1_RowCommand1" >
                <Columns>
                    <asp:HyperLinkField DataNavigateUrlFields="cart_id" 
                        DataNavigateUrlFormatString="CartDetails.aspx?cart_id={0}" 
                        DataTextField="Invoice No" DataTextFormatString='{0}' HeaderText="Request No" 
                        ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center" SortExpression="Request No">
                        <HeaderStyle HorizontalAlign="Center"></HeaderStyle>
                        <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:HyperLinkField>

                    <asp:BoundField DataField="User Name" HeaderText="User Name" 
                        SortExpression="User Name" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center" >
                        <HeaderStyle HorizontalAlign="Center"></HeaderStyle>
                        <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:BoundField>

                    <asp:BoundField DataField="Company" HeaderText="Company" 
                        SortExpression="Company" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center" >
                        <HeaderStyle HorizontalAlign="Center"></HeaderStyle>
                        <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:BoundField>

                    <asp:BoundField DataField="Client User" HeaderText="Client User" 
                        SortExpression="Client User" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center" >
                        <HeaderStyle HorizontalAlign="Center"></HeaderStyle>
                        <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:BoundField>

                    <asp:BoundField DataField="Client Company" HeaderText="Client Company" 
                        SortExpression="Client Company"  ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center">
                        <HeaderStyle HorizontalAlign="Center"></HeaderStyle>
                        <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:BoundField>

                    <asp:BoundField DataField="cart_date" HeaderText="Date" 
                        SortExpression="cart_date" DataFormatString="{0:dd/MM/yyyy}" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center" >
                        <HeaderStyle HorizontalAlign="Center"></HeaderStyle>
                        <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:BoundField>
                            
                    <asp:BoundField DataField="total_price" HeaderText="Total Price" 
                        SortExpression="total_price" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center" >                
                        <HeaderStyle HorizontalAlign="Center"></HeaderStyle>
                        <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:BoundField>
                    <asp:TemplateField HeaderText="" SortExpression="Filepath" ItemStyle-HorizontalAlign="Center">
                        <ItemTemplate>
                            <asp:LinkButton ID="LbPath" runat="server" 
                                Text='Quick View'
                                CommandName="CartView" 
                                ToolTip='<%#Bind("cart_id") %>'
                                CommandArgument='<%#Bind("cart_id") %>'>
                            </asp:LinkButton>
                        </ItemTemplate>
                        <ItemStyle HorizontalAlign="Center"></ItemStyle>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
    </div>
        <br />

        <cc1:ModalPopupExtender ID="ModalPopupExtender1"  runat="server" TargetControlID="Button1" PopupControlID="PnlModal" BackgroundCssClass="modalBackground">
        </cc1:ModalPopupExtender>
        <asp:Button ID="Button1" runat="server" Text="Button" style="visibility:hidden"/>
        
        <asp:Panel ID="PnlModal" runat="server" Width="500px" CssClass="modalPopup">
            
            <asp:GridView ID="GridView2" runat="server" Width="80%" 
            AutoGenerateColumns="False" >
           <Columns>
               <asp:BoundField HeaderText="Service" DataField="item_name" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center"/>
               <asp:BoundField HeaderText="Long Description" DataField="long_description" HtmlEncode="false" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center"/>
               <asp:BoundField HeaderText="Price Schedule" DataField="price_schedule" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center"/>
               <asp:BoundField HeaderText="Price/Unit" DataField="price_per_unit" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center"/>
               <asp:BoundField HeaderText="Qty" DataField="item_count" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center"/>
               <asp:BoundField HeaderText="Total Price" DataField="total_price" ItemStyle-HorizontalAlign="Center" HeaderStyle-HorizontalAlign="Center"/>
           </Columns>
            </asp:GridView>
            <asp:Button ID="Button2" runat="server" Text="Cancel" OnClick="Button2_Click"/>
        </asp:Panel>       
        </div>
</asp:Content>

Code for the command execution is here

protected void GridView1_RowCommand1(object sender, GridViewCommandEventArgs e)
       {
           if (e.CommandName == "CartView")
           {
               LinkButton lt = (LinkButton)sender;
               int cart_id = Convert.ToInt32(lt.CommandArgument);

               adp = new NpgsqlDataAdapter("select item_name,short_description,long_description,unit,price_schedule,price_per_unit,item_count,(price_per_unit*item_count) total_price from im_cart_details a,im_items b where a.item_id=b.item_id and cart_id=" + cart_id, conn);
               dt = new DataTable("items");
               adp.Fill(dt);
               GridView2.DataSource = dt;
               GridView2.DataBind();

               ModalPopupExtender1.Show();
           }
       }

       protected void Button2_Click(object sender, EventArgs e)
       {
           ModalPopupExtender1.Hide();
       }