protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
 {
     switch (e.CommandName)
     {
     case "capnhat":
         gh = new GioHangData();
         DataTable dt = (DataTable)Session["GioHang"];
         foreach (GridViewRow gr in GridView1.Rows)
         {
             TextBox txtsl = (TextBox)gr.FindControl("txtsoluong");
             if (Convert.ToInt32(txtsl.Text) > 0)
             {
                 dt = gh.capNhatlai(dt, double.Parse(txtsl.Text), gr.Cells[1].Text);
             }
             else
             {
                 dt = gh.xoaDong(dt, gr.Cells[1].Text);
                 if (dt.Rows.Count == 0)
                 {
                     Panel2.Visible = true;
                     Panel3.Visible = false;
                 }
             }
         }
         GridView1.DataSource = dt;
         GridView1.DataBind();
         tinhtien(dt);
         Session["GioHang"] = dt;
         break;
     }
 }
    protected void GridView1_RowDeleting(object sender, GridViewDeleteEventArgs e)
    {
        gh = new GioHangData();
        DataTable tb = (DataTable)Session["GioHang"];

        tb = gh.xoaDong(tb, GridView1.Rows[e.RowIndex].Cells[1].Text);
        GridView1.DataSource = tb;
        GridView1.DataBind();
        Session["GioHang"] = tb;
        if (Session["GioHang"] != null)
        {
            DataTable dt = (DataTable)Session["GioHang"];
            if (dt.Rows.Count == 0)
            {
                Panel2.Visible = true;
                Panel3.Visible = false;
            }
        }
    }