private void btnUpdate_Click(object sender, RoutedEventArgs e)
        {
            if (txtQty.Text == "")
            {
                MessageBox.Show("Invalid input!");
                return;
            }

            object id_obj = ((Button)sender).CommandParameter;
            int    id;

            int.TryParse(id_obj.ToString(), out id);

            int  qty;
            bool success = int.TryParse(txtQty.Text, out qty);

            if (success)
            {
                TicketTransactionController.getInstance().update(id, qty);
                MessageBox.Show("Success update transaction!");
            }
            else
            {
                MessageBox.Show("Quantity must be numeric!");
            }

            txtQty.Clear();
            load();
        }
        private void load()
        {
            txtName.Text = "Good to see you back, " + employee.Name + "!";

            viewTransaction.ItemsSource = TicketTransactionController.getInstance().getAll();
            viewTicket.ItemsSource      = TicketController.getInstance().getAll();
            viewPers.ItemsSource        = getPersList();
        }
        private void btnSubmit_Click(object sender, RoutedEventArgs e)
        {
            if (txtQty.Text == "")
            {
                MessageBox.Show("Ticket's quantity must be inputted!");
                return;
            }

            int  qty;
            bool success = int.TryParse(txtQty.Text, out qty);

            if (success)
            {
                TicketTransactionController.getInstance().add(employee.Id, qty);
                MessageBox.Show("Success add transaction!");
            }
            else
            {
                MessageBox.Show("Quantity must be numeric!");
            }

            txtQty.Clear();
            load();
        }