private async void OpenRental_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            var equipment = dgAvailableEquipment.SelectedItem as Equipment;
            var window = new RentalWindow(RentalService, equipment);
            window.ShowDialog();

            // Update the view model.
            ViewModel.AvailableEquipment.Clear();
            ViewModel.Rentals.Clear();
            await LoadDataAsync();
        }
        private async void OpenRental_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            var equipment = dgAvailableEquipment.SelectedItem as Equipment;
            var window    = new RentalWindow(RentalService, equipment);

            window.ShowDialog();

            // Update the view model.
            ViewModel.AvailableEquipment.Clear();
            ViewModel.Rentals.Clear();
            await LoadDataAsync();
        }