private void Window_Loaded(object sender, RoutedEventArgs e)
{
btnCancel.Visibility = Visibility.Hidden;
btnSave.Visibility = Visibility.Hidden;
Performance performance = manager.RetrievePerformanceByID(performanceID);
txtPerformanceName.Text = performance.Name;
txtDescription.Text = performance.Description;
dtpDate.SelectedDate = performance.Date;
}