private void buttonNewUser_Click(object sender, RoutedEventArgs e)
        {
            User newUser = new User
            {
                Email    = textboxNewUser.Text,
                Password = textbox_new_password.Text
            };

            UserManager.GetInstance().AddList(newUser);
            windowSub.ReloadGrid();

            Close();
        }
        private void buttonNewUser_Click(object sender, RoutedEventArgs e)
        {
            Client newClient = new Client
            {
                Name        = txbName.Text,
                Email       = txbEmail.Text,
                PhoneNumber = txbPhone.Text
            };

            ClientManager.GetInstance().AddList(newClient);
            windowSub.ReloadGrid();

            Close();
        }
        private void buttonNewProduct_Click(object sender, RoutedEventArgs e)
        {
            Product newProduct = new Product
            {
                Name    = txbName.Text,
                Value   = float.Parse(txbValue.Text),
                BarCode = int.Parse(txbBarCode.Text)
            };

            ProductManager.GetInstance().AddList(newProduct);
            windowSub.ReloadGrid();

            Close();
        }