How To bind Rows in Dynamically gridview

protected void BindGridDetails()
    {
        try
        {
            int rowIndex = 0;
            for (int i = 0; i < gridview1.Rows.Count; i++)
            {
                TextBox txtcategory = (TextBox)gridview1.Rows[rowIndex].Cells[2].FindControl("txtcategory");
                DropDownList ddlmodel = (DropDownList)gridview1.Rows[rowIndex].Cells[2].FindControl("ddlmodel");
                TextBox txtdescrip = (TextBox)gridview1.Rows[rowIndex].Cells[2].FindControl("txtdescrip");//TextBox txtdescrip = gridview1.FindControl("txtdescrip") as TextBox;
                TextBox txtPrice = (TextBox)gridview1.Rows[rowIndex].Cells[2].FindControl("txtPrice");//TextBox txtPrice = gridview1.FindControl("txtPrice") as TextBox;
                TextBox txtQuantity = (TextBox)gridview1.Rows[rowIndex].Cells[2].FindControl("txtQuantity");//TextBox txtQuantity = gridview1.FindControl("txtQuantity") as TextBox;
                TextBox txtdiscount = (TextBox)gridview1.Rows[rowIndex].Cells[2].FindControl("txtdiscount");//TextBox txtdiscount = gridview1.FindControl("txtdiscount") as TextBox;
                DropDownList ddTax = (DropDownList)gridview1.Rows[rowIndex].Cells[2].FindControl("ddTax");
                TextBox txttaxamt = (TextBox)gridview1.Rows[rowIndex].Cells[2].FindControl("txttaxamt");//TextBox txttaxamt = gridview1.FindControl("txttaxamt") as TextBox;
                TextBox txtTotal = (TextBox)gridview1.Rows[rowIndex].Cells[2].FindControl("txtTotal");//TextBox txtTotal = gridview1.FindControl("txtTotal") as TextBox;
                TextBox tot = (TextBox)gridview1.Rows[rowIndex].Cells[2].FindControl("txttotamt");
                Label lblGrandTotal = (Label)panelGrd.FindControl("lblTotal");

                //string qry = "select distinct category,invoice,tot,model,price,quantity,tax,total,grandtoal,discount,discription,taxamount from Client_Bill_TB where id='" + ViewState["VSID"] + "'";
                string qry = "select distinct category,invoice,tot,model,price,quantity,tax,total,grandtoal,discount,discription,taxamount from Client_Bill_TB where invoice='45/062014'";
                List<Class1> listuser = cbbal.SqlReader(qry);
                if (listuser.ToList().Count > 0)
                {
                    txtcategory.Text = listuser[0].stecategory.ToString();
                    //ddlmodel.DataSource = cbbal.DSet("select distinct model from  Client_Bill_TB where id='" + ViewState["VSID"] + "'");
                    ddlmodel.DataSource = cbbal.DSet("select distinct model from  Client_Bill_TB where invoice='45/062014'");
                    ddlmodel.DataTextField = "model";
                    ddlmodel.DataBind();
                    tot.Text = listuser[0].strtot.ToString();
                    txtdescrip.Text = listuser[0].strdescription.ToString();
                    txtPrice.Text = listuser[0].strprice.ToString();
                    txtQuantity.Text = listuser[0].strquantity.ToString();
                    txtdiscount.Text = listuser[0].strdiscount.ToString();
                    //ddTax.DataSource = cbbal.DSet("select tax,id from  Client_Bill_TB where id='" + ViewState["VSID"] + "'");
                    ddTax.DataSource = cbbal.DSet("select tax,id from  Client_Bill_TB where invoice='45/062014'");
                    ddTax.DataTextField = "tax";
                    ddTax.DataBind();
                    txtInvoice.Text = listuser[0].strInvoice.ToString();
                    txttaxamt.Text = listuser[0].strtaxamount.ToString();
                    txtTotal.Text = listuser[0].strtotal.ToString();
                    lblGrandTotal.Text = listuser[0].strtotalamount.ToString();
                }
                rowIndex++;
            }
        }
        catch (Exception ex)
        {
            string script = "<script type=\"text/javascript\"> window.alert('" + ex.Message + "'); </script>";
            ClientScript.RegisterClientScriptBlock(this.GetType(), "alertscript", script); 
        }
    }