ASP.Net DropDownList ไม่แสดง row ถัดไป เดาน่าจะเกี่ยวกับ Index ครับ

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
    public partial class Creat_Cliam_From_A_Add_labour_Quatation : System.Web.UI.Page
    {
        
       // int rowIndex = 0;  
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                
                SetInitialRow();
                BindDropDownList();
            
            }    

        }

        private void SetInitialRow()
        {
           // BindDropDownList();
            DataTable dt = new DataTable();
            DataRow dr = null;
            dt.Columns.Add(new DataColumn("RowNumber", typeof(string)));
            dt.Columns.Add(new DataColumn("Column1", typeof(string)));
            dt.Columns.Add(new DataColumn("Column2", typeof(string)));
            dt.Columns.Add(new DataColumn("Column3", typeof(string)));
            dt.Columns.Add(new DataColumn("Column4", typeof(string)));
            dt.Columns.Add(new DataColumn("Column5", typeof(string)));
            dt.Columns.Add(new DataColumn("Column6", typeof(string)));
           

            dr = dt.NewRow();
            dr["RowNumber"] = 1;
            dr["Column1"] = string.Empty;
            dr["Column2"] = string.Empty;
            dr["Column3"] = string.Empty;
            dr["Column4"] = string.Empty;
            dr["Column5"] = string.Empty;
            dr["Column6"] = string.Empty;
           

            dt.Rows.Add(dr);
            ViewState["CurrentTable"] = dt;
            Gridview1.DataSource = dt;
            Gridview1.DataBind();

        }//end SetInitialRow
        private void addNewRowToGrid()
        {

            
            SqlConnection con = new SqlConnection("Data Source=OMG-NB;Initial Catalog=DB_Modified;Integrated Security=True");
         
           int rowIndex = 0;
            if (ViewState["CurrentTable"] != null)
            {

                DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
                DataRow drCurrentRow = null;
                if (dtCurrentTable.Rows.Count > 0)
                {
                    for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
                    {
                    
                       
                        DropDownList drop2 = (DropDownList)Gridview1.Rows[rowIndex].Cells[1].FindControl("DropDownList2");
                        TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                        TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
                        TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("TextBox4");
                        TextBox box5 = (TextBox)Gridview1.Rows[rowIndex].Cells[5].FindControl("TextBox5");
                        TextBox box6 = (TextBox)Gridview1.Rows[rowIndex].Cells[6].FindControl("TextBox6");
                       
                        try
                        {
                            
                            Response.Write(drop2);
                            con.Open();


                            SqlCommand cmd = new SqlCommand();
                            cmd.Connection = con;
                         //   Response.Write(drop2.Text);
                           cmd.CommandText = "INSERT INTO [dbo].[Labour]([LaborCode],[Work code],[LaborName],[ModelCar],[LabourHour],[Group])VALUES('" + drop2.SelectedIndex+ "','" + box2.Text + "','" + box3.Text + "','" + box4.Text + "','" + box5.Text + "','" + box6.Text + "')";



       

                            cmd.ExecuteNonQuery();
                        
                       
                           
                          con.Close();

                        }
                        catch
                        {
              



                        }
                        
                        drCurrentRow = dtCurrentTable.NewRow();
                        drCurrentRow["RowNumber"] = i + 1;

                       dtCurrentTable.Rows[i - 1]["Column1"] = drop2.Text;
                        dtCurrentTable.Rows[i - 1]["Column2"] = box2.Text;
                        dtCurrentTable.Rows[i - 1]["Column3"] = box3.Text;
                        dtCurrentTable.Rows[i - 1]["Column4"] = box4.Text;
                        dtCurrentTable.Rows[i - 1]["Column5"] = box5.Text;
                        dtCurrentTable.Rows[i - 1]["Column6"] = box6.Text;
                    
                        rowIndex++;
                   
                     
                      
                    }//end for 
                    dtCurrentTable.Rows.Add(drCurrentRow);
                    ViewState["CurrentTable"] = dtCurrentTable;

                    Gridview1.DataSource = dtCurrentTable;
                    Gridview1.DataBind();        
                }//end if
            }//end if
            else
           {
                Response.Write("ViewState is null");
           }
            //Set Previous Data on Postbacks
           SetPreviousData();
        }//end addNewRowToGrid
        private void SetPreviousData()
        {
            int rowIndex = 0;
            if (ViewState["CurrentTable"] != null)
            {
                DataTable dt = (DataTable)ViewState["CurrentTable"];
                if (dt.Rows.Count > 0)
                {
                    for (int i = 0; i < dt.Rows.Count; i++)
                    {
                        DropDownList drop2 = (DropDownList)Gridview1.Rows[rowIndex].Cells[1].FindControl("DropDownList2");
                        TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                        TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
                        TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("TextBox4");
                        TextBox box5 = (TextBox)Gridview1.Rows[rowIndex].Cells[5].FindControl("TextBox5");
                        TextBox box6 = (TextBox)Gridview1.Rows[rowIndex].Cells[6].FindControl("TextBox6");
                    



                        drop2.Text = dt.Rows[i]["Column1"].ToString();
                        box2.Text = dt.Rows[i]["Column2"].ToString();
                        box3.Text = dt.Rows[i]["Column3"].ToString();
                        box4.Text = dt.Rows[i]["Column4"].ToString();
                        box5.Text = dt.Rows[i]["Column5"].ToString();
                        box6.Text = dt.Rows[i]["Column6"].ToString();
                        rowIndex++;
                 
                       

                    }
                    //BindDropDownList();
                }
                
            }
        }

        protected void ButtonAdd_Click(object sender, EventArgs e)
        {
            addNewRowToGrid();
      
            BindDropDownList();
            
            
            
            
        }

        protected void Button7_Click(object sender, EventArgs e)
        {
            OpenNewWindow("result_labour_search.aspx");
        }//end med
        public void OpenNewWindow(string url)
        {

            ClientScript.RegisterStartupScript(this.GetType(), "newWindow", String.Format("<script>window.open('{0}');</script>", url));

        }

        private void BindDropDownList()
        {
            int rowIndexa = 0;
            
           // DropDownLrowIndexaist ddlCountries = Gridview1.FooterRow.FindControl("ddlCountries") as DropDownList;
           // TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");

            SqlConnection connection = new SqlConnection("Data Source=OMG-NB;Initial Catalog=DB_Modified;Integrated Security=True");
            try
            {
                DataTable dt = new DataTable();
                string LaborCode = string.Empty;
                string Workcodee = string.Empty;
                string ModelCar = string.Empty;
                string Equipment = string.Empty;
                string newName = string.Empty;
                

                connection.Open();
                string sqlStatement = "SELECT * FROM Labour";
                SqlCommand sqlCmd = new SqlCommand(sqlStatement, connection);
                SqlDataAdapter sqlDa = new SqlDataAdapter(sqlCmd);
                
                int a = 0;
                sqlDa.Fill(dt);
               if (dt.Rows.Count > 0)
                {
                    for (int i = 0; i <= dt.Rows.Count; i++)
                    {
                            LaborCode = dt.Rows[i]["LaborCode"].ToString();
                            Workcodee = dt.Rows[i]["Work code"].ToString();
                            ModelCar = dt.Rows[i]["ModelCar"].ToString();
                            Equipment = dt.Rows[i]["Equipment"].ToString();

                            newName = LaborCode + " ---- " + Workcodee + "   | " + ModelCar + "   | " + Equipment;
                            DropDownList drop2 = (DropDownList)Gridview1.Rows[rowIndexa].Cells[1].FindControl("DropDownList2");
                            drop2.Items.Add(new ListItem(newName, LaborCode));
                          //  
                  
                    }
                    rowIndexa++;
                      
                }
                

            }
            catch (System.Data.SqlClient.SqlException ex)
            {
                string msg = "Fetch Error:";
                msg += ex.Message;
                throw new Exception(msg);
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message.ToString());
            }
            finally
            {
               // connection.Close();
            }
        }




    }//end class
}