On button click add element to grid view using List

List<DOBillDetails> listDOBillDetails = new List<DOBillDetails>();

protected void btnAdd_Click(object sender, EventArgs e)
{

try
{


DOBillDetails objDOBillDetail = new DOBillDetails();
objDOBillDetail.ProductId = Convert.ToInt32(ddProductName.SelectedValue);
objDOBillDetail.Description = Convert.ToString(txtDescription.Text);
objDOBillDetail.Unit = Convert.ToInt32(txtUnit.Text);
objDOBillDetail.Qty = Convert.ToInt32(txtQty.Text);
objDOBillDetail.UnitPrice = Convert.ToInt32(txtUnitPrice.Text);
objDOBillDetail.TaxPer = Convert.ToString(txtTaxPer.Text);
objDOBillDetail.Discount = Convert.ToString(txtDiscount.Text);
objDOBillDetail.Total = Convert.ToInt32(txtTotal.Text);

listDOBillDetails.Add(objDOBillDetail);

//dtgBill.DataSource = objBLLBillDetails.FillGrid(ddProductName.SelectedValue, txtDescription.Text, txtUnit.Text,
//txtQty.Text,txtUnitPrice.Text, txtTaxPer.Text, txtDiscount.Text, txtTotal.Text);
dtgBill.DataSource = listDOBillDetails;
dtgBill.DataBind();
}
catch (Exception ex)
{
throw;
}
}