Print only CheckBox Checked ( Selected ) records of GridView in ASP.Net

    <asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
        runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:CheckBox ID = "CheckBox1" runat="server" />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:BoundField DataField="Name" HeaderText="Name" ItemStyle-Width="150" />
            <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="150" />
        </Columns>
    </asp:GridView>
    <br />
    <asp:Button ID="btnPrint" runat="server" Text="Print" 
        onclick="btnPrint_Click" />

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            DataTable dt = new DataTable();
            dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id"), new DataColumn("Name"), new DataColumn("Country") });
            dt.Rows.Add(1, "John Hammond", "United States");
            dt.Rows.Add(2, "Mudassar Khan", "India");
            dt.Rows.Add(3, "Suzanne Mathews", "France");
            dt.Rows.Add(4, "Robert Schidner", "Russia");
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
    }

    protected void btnPrint_Click(object sender, EventArgs e)
    {
        foreach (GridViewRow row in GridView1.Rows)
        {
            row.Visible = (row.FindControl("CheckBox1") as CheckBox).Checked;
        }
        StringWriter sw = new StringWriter();
        HtmlTextWriter hw = new HtmlTextWriter(sw);
        GridView1.RenderControl(hw);
        string html = sw.ToString().Replace("\"", "'").Replace(System.Environment.NewLine, "");
        StringBuilder sb = new StringBuilder();
        sb.Append("<script type = 'text/javascript'>");
        sb.Append("window.onload = new function(){");
        sb.Append("var printWin = window.open('', '', 'left=0");
        sb.Append(",top=0,width=1000,height=600,status=0');");
        sb.Append("if(printWin == null) return;");
        sb.Append("printWin.document.write(\"");
        sb.Append(html);
        sb.Append("\");");
        sb.Append("printWin.document.close();");
        sb.Append("printWin.focus();");
        sb.Append("printWin.print();printWin.opener.location.href=printWin.opener.location.href;");
        sb.Append("printWin.close();};");
        sb.Append("</script>");
        ClientScript.RegisterStartupScript(this.GetType(), "GridPrint", sb.ToString());
    }
    public override void VerifyRenderingInServerForm(Control control)
    {
        /* Verifies that the control is rendered */
    }

using System.Data;
using System.Text;
using System.IO;