private void button_Click(object sender, RoutedEventArgs e)
        {
            try
            {
                FlatPurchaseViewModel vm = DataContext as FlatPurchaseViewModel;

                if (vm.Register())
                {
                    MessageBox.Show("Нову заявку на продаж квартири додано в базу");
                }
            }
            catch (Exception exc)
            {
                MessageBox.Show(exc.Message);
            }
        }
 private void Window_Loaded(object sender, RoutedEventArgs e)
 {
     DataContext = new FlatPurchaseViewModel();
 }