How to Bind data in gridview when Item selectd in DropdownList

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C#

ASP.NET

Hello Expert(s),

I have Three(3) dropdownLists(ddl),
When User Select 1st ddl, 2nd ddl will be enabled and when 3rd ddl is selected than Gridview will be visible on bases of 3rd ddl's ID .I Completed my task at 3rd ddl but when I select item in 3rd ddl gridview is not getting visible .Please help me who knows answer.please reply me .thanks In Advance!!!!!

My Code Behind are given below:

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                ddlFaculty.DataSource = GetData("spGetFaculty", null);
                ddlFaculty.DataBind();


                ListItem liFaculty = new ListItem("Select Faculty", "-1");
                ddlFaculty.Items.Insert(0, liFaculty);

                ListItem liSubject = new ListItem("Select Subject", "-1");
                ddlSubject.Items.Insert(0, liSubject);

                ListItem liSupervisor = new ListItem("Select Supervisor", "-1");
                ddlSupervisor.Items.Insert(0, liSupervisor);


                ddlSubject.Enabled = false;
                ddlSupervisor.Enabled = false;

                
                //ThesisAwardGridView.Visible = false;

            }

        }
        private DataSet GetData(string SPName, SqlParameter SPParam)
        {
            string cs = ConfigurationManager.ConnectionStrings["DPSMLSU"].ConnectionString;
            SqlConnection con = new SqlConnection(cs);
            SqlDataAdapter da = new SqlDataAdapter(SPName, con);
            DataTable dt = new DataTable();
            da.SelectCommand.CommandType = CommandType.StoredProcedure;
            if (SPParam != null)
            {
                da.SelectCommand.Parameters.Add(SPParam);
            }
            DataSet DS = new DataSet();
            da.Fill(DS);
            return DS;
        }

        protected void ddlFaculty_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (ddlFaculty.SelectedIndex == 0)
            {
                ddlSubject.SelectedIndex = 0;
                ddlSubject.Enabled = false;

                ddlSupervisor.SelectedIndex = 0;
                ddlSupervisor.Enabled = false;
            }
            else
            {
                ddlSubject.Enabled = true;
                SqlParameter parameter = new SqlParameter("@FacultyId ", ddlFaculty.SelectedValue);
                DataSet DS = GetData("spGetSubjectByFacultyId", parameter);

                ddlSubject.DataSource = DS;
                ddlSubject.DataBind();

                ListItem liSubject = new ListItem("Select Subject", "-1");
                ddlSubject.Items.Insert(0, liSubject);

                ddlSupervisor.SelectedIndex = 0;
                ddlSupervisor.Enabled = false;
            }
        }

        protected void ddlSubject_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (ddlSubject.SelectedIndex == 0)
            {
                ddlSupervisor.SelectedIndex = 0;
                ddlSupervisor.Enabled = false;

            }
            else
            {
                ddlSupervisor.Enabled = true;
                SqlParameter parameter = new SqlParameter("@SubjectId ", ddlSubject.SelectedValue);
                DataSet DS = GetData("spGetSupervisorListBySubjectId ", parameter);

                ddlSupervisor.DataSource = DS;
                ddlSupervisor.DataBind();

                ListItem liSupervisor = new ListItem("Select Supervisor", "-1");
                ddlSupervisor.Items.Insert(0, liSupervisor);

               LoadGirdView();

            }
        }

        private void LoadGirdView()
        {

            SqlParameter parameter = new SqlParameter("@supervisorId", ddlSupervisor.SelectedValue);
            DataSet DS = GetData("sp1GetThesisAwardedBySupervisorId", parameter);
            ThesisAwardGridView.DataSource = DS;
            ThesisAwardGridView.DataBind();
        }
        

        
    }
}