private void BuyTicket(object sender, RoutedEventArgs e)
{
var button = sender as Button;
var performance = button.CommandParameter as Performance;
BuyTicket buyTicket = new BuyTicket(performance);
this.Content = buyTicket;
}
private void Quantity_TextChanged(object sender, TextChangedEventArgs e)
{
if (_parent is null)
{
_parent = FindParent <BuyTicket>(this);
}
_parent.MakeSum();
}