Add GridView data to Custom Business Object List in ASP.Net

Hi This is My Method,Hear How to get Checkbox Value from Gridview and adde that value inti list?

 private List<ActivityList> PopulateData()
        {
            string ActivityCode = string.Empty;
            string ActivityName = string.Empty;
            List<ActivityList> list = (List<ActivityList>)Session["ActivityToStudent"];
            List<ActivityList> listObj = (List<ActivityList>)Session["ActivityToStudent"];
            for (int j = 0; j < listObj.Count; j++)
            {
                ActivityCode = listObj[j].ActivityCode;
                ActivityName = listObj[j].ActivityName;


                int Count = list.Count;
                list.Clear();
                for (int i = 0; i < Count; i++)
                {
                    ActivityList TermListObj = new ActivityList();

                    CheckBox ChkStatus =
                                  (CheckBox)grvStudentDetails.Rows[i].Cells[4].FindControl("Gts_SMS_Trans_ActToStu_chk_Status");

                 
                   
                    TermListObj.CheckStatus = Convert.ToBoolean(ChkStatus.Checked);

                    TermListObj.ActivityCode = ActivityCode;
                    TermListObj.ActivityName = ActivityName;
                    list.Add(TermListObj);
                }
            }

            return list;
        }