private void B_add_account_Click(object sender, RoutedEventArgs e)
        {
            //generowanie losowego numeru konta
            int    nraccount = 0;
            Random rnd       = new Random();

            nraccount = rnd.Next(10000, 99999);

            //sprawdzenie czy konto o wylosowanym numerze istnieje, jesli tak to generuj nowy nr
            foreach (KeyValuePair <Account, Customer> o in kk.List_Account)
            {
                if (o.Key.Number.Equals(nraccount) == true)
                {
                    nraccount = rnd.Next(10000, 99999);
                }
            }

            AccountWindow new_account = new AccountWindow();

            if (CB_list_customers.SelectedIndex >= 0)
            {
                Customer k = CB_list_customers.SelectedItem as Customer; // rzutowanie na klasę klient
                new_account.TB_nraccount_generate.Text = nraccount.ToString();
                new_account.ShowDialog();

                //nkonto.Owner = this; // potrzebne by z okna podrzednego można było odwoalc się do zasobów MainWindow

                if (new_account.DialogResult == true)
                {
                    switch (new_account.CB_type_account.Text.ToString())
                    {
                    case "ROR":
                        Account NewKonto = new ROR(nraccount, 0);
                        kk.Plus(NewKonto, k);
                        break;

                    case "Lokata":
                        Account NewKonto1 = new Investment(nraccount, 0);
                        kk.Plus(NewKonto1, k);
                        break;

                    case "Karta kredytowa":
                        Account NewKonto2 = new CreditCard(nraccount, 0);
                        kk.Plus(NewKonto2, k);
                        break;
                    }
                }
            }
            UpdateListBox();
        }
        public MainWindow()
        {
            InitializeComponent();

            Customer k1 = new Customer("Kowalski", "Jan");
            Customer k2 = new Customer("Nowak", "Andrzej");
            Customer k3 = new Customer("Bencławski", "Witalis");

            Account ror1 = new ROR(1234, 1500);
            Account ror2 = new ROR(4321, 2500);
            Account ror3 = new ROR(1111, 3200);

            Account lokata1 = new Investment(5678, 1000);
            Account lokata2 = new Investment(8765, 500);
            Account lokata3 = new Investment(2222, 200);

            Account karta1 = new CreditCard(3333, 1020);
            Account karta2 = new CreditCard(4444, 5000);
            Account karta3 = new CreditCard(5555, 2000);

            kk.Plus(ror1, k1);
            kk.Plus(ror2, k2);
            kk.Plus(ror3, k3);

            kk.Plus(lokata1, k1);
            kk.Plus(lokata2, k2);
            kk.Plus(lokata3, k3);

            kk.Plus(karta1, k1);
            kk.Plus(karta2, k2);
            kk.Plus(karta3, k3);

            lk.Plus(k2);
            lk.Plus(k3);
            lk.Plus(k1);

            UpdateComboBox();
        }