asp.net webform pass parameter by session

//enroll.cs

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

namespace CttiDemo

{

    public partial class Enrollment : System.Web.UI.Page

    {

        List<int> courses = null;

        protected void Page_Load(object sender, EventArgs e)

        {

            //get the id collection from session and if it doesn't exist we add it

            if (Session["courses"] != null)

                courses = (List<int>)Session["courses"];

            else

                courses = new List<int>();

        }

        protected void uxEnrol_Click(object sender, EventArgs e)

        {

            //get the course id from the drop down and add the value to the list

            var id = int.Parse(uxCourses.SelectedValue);

            courses.Add(id);

            //add the list to the session

            Session["courses"] = courses;

            //or

            //Session.Add("courses", courses);

        }

    }

}

-----------------------------------------------------------

//payment.cs

using Ctti.Data;

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

namespace CttiDemo

{

    public partial class Payment : System.Web.UI.Page

    {

        protected void Page_Load(object sender, EventArgs e)

        {

            if (!IsPostBack)

            {

                //get the courses id collection from session if it exists

                if(Session["courses"] != null)

                {

                    var courses = (List<int>)Session["courses"];

                    var db = new CTTIEntities1();

                    var list = db.Courses.Where(c => courses.Contains(c.Id)).ToList();

                    uxCourses.DataSource = list;

                    uxCourses.DataBind();

                    //uxCourses.Columns[0].Visible = false;

                }

            }

        }

        protected void uxCourses_PreRender(object sender, EventArgs e)

        {

            if (uxCourses.Columns.Count > 0)

                uxCourses.Columns[0].Visible = false;

        }

        //This is the event to capture when each row is being added and...

        protected void uxCourses_RowDataBound(object sender, GridViewRowEventArgs e)

        {

            //...make the first cell of the row being added invisible!!!

            e.Row.Cells[0].Visible = false;

        }

    }

}