Filter ListView with Preserving the Last Searched Records ASP.Net

This way:

HTML

<form id="form1" runat="server">
<div>
    <asp:TextBox ID="txtId" runat="server" OnTextChanged="Search" AutoPostBack="true" />    
    <asp:ListView ID="ListView1" runat="server" ItemPlaceholderID="itemPlaceHolder1"
        GroupPlaceholderID="groupPlaceHolder1">
        <LayoutTemplate>
            <table cellpadding="2" cellspacing="2">
                <tr>
                    <th>
                        Prouct Name
                    </th>
                    <th>
                        Qty
                    </th>
                    <th>
                        Price
                    </th>
                    <th>
                        VAT
                    </th>
                </tr>
                <asp:PlaceHolder runat="server" ID="groupPlaceHolder1"></asp:PlaceHolder>
            </table>
        </LayoutTemplate>
        <GroupTemplate>
            <tr>
                <asp:PlaceHolder runat="server" ID="itemPlaceHolder1"></asp:PlaceHolder>
            </tr>
        </GroupTemplate>
        <ItemTemplate>
            <td>
                <%# Eval("ProductName")%>
            </td>
            <td>
                <%# Eval("Quantity")%>
            </td>
            <td>
                <%# Eval("Price")%>
            </td>
            <td>
                <%# Eval("Vat")%>
            </td>
        </ItemTemplate>
    </asp:ListView>
</div>
</form>

Namespace

using System.Configuration;
using System.Data.SqlClient;
using System.Data;

 C#

protected void Search(object sender, EventArgs e)
{
    BindListView();
}

private void BindListView()
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand())
        {
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                cmd.CommandText = "SELECT * FROM tblProduct WHERE Id = @Id";
                cmd.Connection = con;
                cmd.Parameters.AddWithValue("@Id", Convert.ToInt32(this.txtId.Text.Trim()));
                DataTable dt = new DataTable();
                sda.Fill(dt);
                DataTable products = new DataTable();
                if (ViewState["Products"] == null)
                {
                    products.Merge(dt, true);
                }
                else
                {
                    products = (DataTable)ViewState["Products"];
                    products.Merge(dt, true);
                }

                ViewState["Products"] = products;
                ListView1.DataSource = products;
                ListView1.DataBind();
            }
        }
    }
}

Screenshot