private void SavePeriodButton_Click(object sender, RoutedEventArgs e) { if (!ReportedDatePicker.SelectedDate.HasValue || !Decimal.TryParse(xRateUSDToUAHTextBox.Text, out decimal xRateUSD) || !Decimal.TryParse(xRateEURToUAHTextBox.Text, out decimal xRateEUR)) { return; } PeriodSummary newPeriodSummary = new PeriodSummary(ReportedDatePicker.SelectedDate.Value, xRateUSD, xRateEUR); PeriodSummary result = _summaryService.AddPeriod(newPeriodSummary); Periods.Add(result); PeriodsListView.ItemsSource = Periods.OrderByDescending(p => p.ReportedDate); }