Dynamic Dropdownlist

Hi I am developing dynamic table with dropdown list when i click on add button it will show one dynamic table with Add button for creating another dynamic table i will fill data and stored in database

look on my code below



   private void AddNewRowToGrid()
    {
        int rowIndex = 0;
        if (ViewState["CurrentTable"] != null)
        {
            DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
            DataRow drCurrentRow = null;
            if (Gridview1.Rows.Count > 0)
            {
                int intRow = Gridview1.Rows.Count;
                DropDownList val1 = (DropDownList)Gridview1.Rows[intRow - 1].Cells[1].FindControl("txtItemCode");

                
                TextBox val2 = (TextBox)Gridview1.Rows[intRow - 1].Cells[2].FindControl("txtDescription");
                TextBox val3 = (TextBox)Gridview1.Rows[intRow - 1].Cells[3].FindControl("txtUOM");
                TextBox val4 = (TextBox)Gridview1.Rows[intRow - 1].Cells[4].FindControl("txtRequestQty");
            //  TextBox val5 = (TextBox)Gridview1.Rows[intRow - 1].Cells[5].FindControl("txtAmount");
               
                    for (int i = 0; i < Gridview1.Rows.Count; i++)
                    {
                        //extract the TextBox values
                        //Label lblSno = (Label)Gridview1.Rows[rowIndex].Cells[0].FindControl("lblSno");
                        DropDownList box1 = (DropDownList)Gridview1.Rows[rowIndex].Cells[1].FindControl("txtItemCode");
                        TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("txtDescription");
                        TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("txtUOM");
                        TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("txtRequestQty");
                   //  TextBox box5= (TextBox)Gridview1.Rows[rowIndex].Cells[5].FindControl("txtAmount");

                        //dtCurrentTable.Rows[i][strSno] = lblSno.Text;
                        dtCurrentTable.Rows[i][ItemCode] = box1.Text;
                        dtCurrentTable.Rows[i][strDescription] = box2.Text;
                        dtCurrentTable.Rows[i][UOM] = box3.Text;
                        dtCurrentTable.Rows[i][RequestQty] = box4.Text;
                      //  dtCurrentTable.Rows[i][Amount] = (Convert.ToInt32(box3.Text.ToString().Trim()) * Convert.ToInt32(box4.Text.ToString().Trim()));

                        rowIndex++;
                    }
                    drCurrentRow = dtCurrentTable.NewRow();

                    //add new row to DataTable
                    dtCurrentTable.Rows.Add(drCurrentRow);

                    for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
                    {
                        // DataRow dr = null;
                        //dr[strSno] = i;
                        dtCurrentTable.Rows[i - 1][strSno] = i;
                    }
                    dtCurrentTable.AcceptChanges();
                    //Store the current data to ViewState
                    ViewState["CurrentTable"] = dtCurrentTable;
                    //Rebind the Grid with the current data
                    Gridview1.DataSource = dtCurrentTable;
                    Gridview1.DataBind();
            }
        }
        else
        {
            Response.Write("ViewState is null");
        }
    }
    protected void ButtonAdd_Click(object sender, EventArgs e)
    {
        AddNewRowToGrid();
    }

   
99% of my code is fine but when I click on add button for creating new dynamic table  the first table dropdown selected item changed to first list item how to maintain view state?