ASP.Net เลือก dropdownlist แล้ว gridview หรือ chart ไม่เปลี่ยนแปลงตามที่เราเลือกค่ะ C#

 protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                string query = "SELECT [level], [G1] FROM [Table1]";
                DataTable dt = GetData(query);
                DropDownList1.DataSource = dt;
                DropDownList1.DataTextField = "level";
                DropDownList1.DataValueField = "level";
                DropDownList1.DataBind();
                GridView1.DataSource = dt;
                GridView1.DataBind();
                DropDownList1.Items.Insert(0, new ListItem("Select", ""));
                
            }
        }

        protected void Chart1_Load(object sender, EventArgs e)
        {
            DataTable dt = new DataTable();
            string connetionString = null;
            OleDbConnection connection;
            OleDbDataAdapter oledbAdapter;
            DataSet ds = new DataSet();
            string firstSql = null;
            string secondSql = null;

            string strPath = System.IO.Directory.GetCurrentDirectory();
            connetionString = "Provider=Microsoft.ACE.OLEDB.12.0;"
                        + "Data Source=" + strPath + "\\DatabaseChart.accdb;"
                        + "Persist Security Info=False;";
            firstSql = "SELECT * FROM [Table1]";
            secondSql = "SELECT * FROM [Table2]";
            connection = new OleDbConnection(connetionString);

            connection.Open();
            oledbAdapter = new OleDbDataAdapter(secondSql, connection);
            oledbAdapter.Fill(dt);
            Chart1.DataSource = dt;
            Chart1.DataBind();
           
        }
        private static DataTable GetData(string query)
        {
            DataTable dt = new DataTable();
            string connetionString = null;
            OleDbConnection connection;
            OleDbDataAdapter oledbAdapter;
            DataSet ds = new DataSet();
            string firstSql = null;
            string secondSql= null;
           
            string strPath = System.IO.Directory.GetCurrentDirectory();
            connetionString = "Provider=Microsoft.ACE.OLEDB.12.0;"
                        + "Data Source=" + strPath + "\\DatabaseChart.accdb;"
                        + "Persist Security Info=False;";
            firstSql = "SELECT * FROM [Table1]";
            secondSql = "SELECT * FROM [Table2]";
            connection = new OleDbConnection(connetionString);

            connection.Open();
            oledbAdapter = new OleDbDataAdapter(firstSql, connection);
            oledbAdapter.Fill(dt);
            return dt;

            
        }

        protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (DropDownList1.SelectedIndex == 1)
            {
                DataTable dt = new DataTable();
                string connetionString = null;
                OleDbConnection connection;
                OleDbDataAdapter oledbAdapter;
                DataSet ds = new DataSet();
                string firstSql = null;
                string secondSql = null;

                string strPath = System.IO.Directory.GetCurrentDirectory();
                connetionString = "Provider=Microsoft.ACE.OLEDB.12.0;"
                            + "Data Source=" + strPath + "\\DatabaseChart.accdb;"
                            + "Persist Security Info=False;";
                firstSql = "SELECT * FROM [Table1]";
                secondSql = "SELECT * FROM [Table2]";
                connection = new OleDbConnection(connetionString);

                connection.Open();
                oledbAdapter = new OleDbDataAdapter(secondSql, connection);
                oledbAdapter.Fill(dt);
                GridView1.DataSource = dt;
                GridView1.DataBind();
            }