private void BtnNew_Click(object sender, RoutedEventArgs e)
{
RentalDataEntry newWin = new RentalDataEntry();
newWin.ShowDialog();
UpdateList();
}
private void EditButton_Click(object sender, RoutedEventArgs e)
{
Button button = sender as Button;
Rental rental = button.DataContext as Rental;
int index = lvRentalList.Items.IndexOf(rental);
RentalDataEntry win = new RentalDataEntry(rental, false);
win.ShowDialog();
UpdateList(index);
}