private void btnClear_Click(object sender, RoutedEventArgs e)
{
RentalServiceClient service = new RentalServiceClient();
tbLicensePlate.Text = "";
tbManufacturer.Text = "";
tbModel.Text = "";
tbYear.Text = "";
tbKmClock.Text = "";
cobFuel.Text = "";
tbColor.Text = "";
cbAvailable.IsChecked = false;
tbRentalPricePerDay.Text = "";
tbRentalPricePerHour.Text = "";
tbSeats.Text = "";
tbVIN.Text = "";
tbCarFilter.Text = "";
tbImagePath.Text = "";
dgCar.SelectedIndex = -1;
tbCarID.Text = Convert.ToString(service.NextCarId());
ImageViewer.Source = null;
btnSave.IsEnabled = false;
btnDelete.IsEnabled = false;
btnAdd.IsEnabled = true;
btnDeleteImage.IsEnabled = false;
}