private void BtnSave_Click(object sender, RoutedEventArgs e)
        {
            if (ValidateFields())
            {
                fuelPurchases.Edit(selected, decimal.Parse(tbCost.Text), double.Parse(tbLitres.Text), (DateTime)dpDate.SelectedDate);
                Refresh();

                changes = true;

                lvItems.UnselectAll();
                SetSelectedToFields(true);

                if (addMode)
                {
                    ToggleAddMode(false);
                }
                else
                {
                    ToggleEditMode(false);
                }
            }
        }