How to fill datagrid only once? it is filled repeatedly...

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;


namespace Petrol_Billing_System1
{
    public partial class frmDisplayCreditSales : Form
    {
        public frmDisplayCreditSales()
        {
            InitializeComponent();
        }

        SqlConnection con = new SqlConnection(Properties.Settings.Default.dbconnection);
        DataSet ds = new DataSet();
       

        private void btnNew_Click(object sender, EventArgs e)
        {
            frmCreditSalesDetails frm = new frmCreditSalesDetails();
            frm.Show();
        }

        private void frmDisplayCreditSales_Load(object sender, EventArgs e)
        {
            dtpdisCreditSale.Value = new DateTime(DateTime.Now.Year, DateTime.Now.Month, DateTime.Now.Day);
            dtpdisCreditSale.CustomFormat = "dd MMMM,yyyy";
            dtpdisCreditSale.Format = DateTimePickerFormat.Custom;

            dtpFromDate.CustomFormat = "dd MMMM,yyyy";
            dtpFromDate.Format = DateTimePickerFormat.Custom;

            dtpToDate.CustomFormat = "dd MMMM,yyyy";
            dtpToDate.Format = DateTimePickerFormat.Custom;

            SqlDataAdapter daitems = new SqlDataAdapter("Select ItemID,ItemName from Items", con);
            daitems.Fill(ds, "items");

            SqlDataAdapter dacust = new SqlDataAdapter("Select CustomerID,CustomerName from Customers", con);
            dacust.Fill(ds,"cust");
                            
            SqlDataAdapter dadt = new SqlDataAdapter("select s.SalesID,c.CustomerID,chd.SalesID,chd.ItemID,ch.ChallanID,ch.Date,s.FromDate,s.ToDate,chd.ItemName,chd.Description,chd.Rate,chd.Qty,(chd.Rate*chd.Qty) as Total from Challans ch inner join ChallanDetails chd on chd.ChallanID=ch.ChallanID inner join  Sales s on s.CustomerID=ch.CustomerID inner join  Customers c on c.CustomerID=s.CustomerID", con);
            dadt.Fill(ds, "dt");

            bndSoDisCrSale.DataSource = ds;
            bndSoDisCrSale.DataMember = "dt";

            cmbCustomerName.DisplayMember = "CustomerName";
            cmbCustomerName.ValueMember = "CustomerID";
            cmbCustomerName.DataSource = ds.Tables["cust"];

           
           txtInvoiceNo.DataBindings.Add("Text", bndSoDisCrSale, "SalesID");
           dtpdisCreditSale.DataBindings.Add("Value", bndSoDisCrSale, "Date");
           cmbCustomerName.DataBindings.Add("SelectedValue", bndSoDisCrSale,"CustomerID");
           dtpFromDate.DataBindings.Add("Value", bndSoDisCrSale, "FromDate");
           dtpToDate.DataBindings.Add("Value", bndSoDisCrSale, "ToDate");


           string sql = string.Format("select ch.Date,ch.ChallanID,chd.ItemName,chd.Description,chd.Rate,chd.Qty,(chd.Rate*chd.Qty) as Total  from ChallanDetails chd inner join challans ch on  ch.ChallanID=chd.ChallanID where chd.SalesID='{0}'", txtInvoiceNo.Text);
           SqlDataAdapter da = new SqlDataAdapter(sql, con);
           da.Fill(ds, "gd");

           grddiscrsale.DataSource = ds;
           grddiscrsale.DataMember = "gd";

          
          ds.Tables["gd"].RowChanged += new DataRowChangeEventHandler(frmDisplayCreditSales_RowChanged);
          
          int total = 0;
          for (int i = 0; i <= grddiscrsale.Rows.Count - 2; i++)
          {
              total += int.Parse(grddiscrsale.Rows[i].Cells["Total"].Value.ToString());
          }

          txtTotalPrice.Text = total.ToString();
 

        }

                    
         void frmDisplayCreditSales_RowChanged(object sender, DataRowChangeEventArgs e)
        {
            decimal Total = 0;

            foreach (DataRow row in ds.Tables["gd"].Rows)
            {

                Total += decimal.Parse(row["Total"].ToString());
            }
            txtTotalPrice.Text = Total.ToString();
        }

        
        private void btnClose_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void btnEdit_Click(object sender, EventArgs e)
        {
            string sql = string.Format("Select SalesID from ChallanDetails where SalesID='{0}'",txtInvoiceNo.Text);
            SqlCommand cmd = new SqlCommand(sql, con);
            SqlDataReader sdr;
            con.Open();
            sdr = cmd.ExecuteReader();
            sdr.Read();
            string salesID = sdr["SalesID"].ToString();
            sdr.Close();
            con.Close();


            frmEditCreditSalesDetails frm= new frmEditCreditSalesDetails(txtInvoiceNo.Text,this);
            frm.Show();
        }

        private void bndnavdiscrsale_RefreshItems(object sender, EventArgs e)
        {
            int total = 0;
            for (int i = 0; i <= grddiscrsale.Rows.Count - 2; i++)
            {
                total += int.Parse(grddiscrsale.Rows[i].Cells["Total"].Value.ToString());

            }

          txtTotalPrice.Text = total.ToString();    
     
          
       }