Need to affect Last Enter Value in viewstate in asp.net RSS

private void BindListView()

{

string constr = ConfigurationManager.AppSettings["s"].ToString();

using (SqlConnection con = new SqlConnection(constr))

{

using (SqlCommand cmd = new SqlCommand())

{

using (SqlDataAdapter sda = new SqlDataAdapter(cmd))

{

cmd.CommandText = "SELECT distinct sectionname,lotno,Productname,mrp from purchasedummy where lotno='" + txtBarcode.Text + "'";

cmd.Connection = con;

//cmd.Parameters.AddWithValue("@PurchaseNo", Convert.ToInt32(this.barcodetx.Text.Trim()));

//cmd.Parameters.AddWithValue("@Qty", Convert.ToInt32(this.qty.Text.Trim()));

DataTable dt = new DataTable();

sda.Fill(dt);

DataTable products = new DataTable();

if (ViewState["Products"] == null)

{

products.Merge(dt, true);

}

else

{

products = (DataTable)ViewState["Products"];

products.Merge(dt, true);

}

ViewState["Products"] = products;

ddsales.DataSource = products;

ddsales.DataBind();

}

}

}

}

protected void txtqty_TextChanged(object sender, EventArgs e)

{

foreach (GridViewRow rowz in ddsales.Rows)

{

double mr, wt, totlrp;

mr =Convert.ToDouble((rowz.FindControl("lblmrp") as Label).Text);

wt = double.Parse(txtqty.Text);

totlrp = mr * wt;

(rowz.FindControl("lblmrp") as Label).Text = Convert.ToString(totlrp);

}

txtqty.Text = "1";

}