private void SendButtonClick(object sender, RoutedEventArgs e)
 {
     content = "Wysłano kod: " + BarCodeTextBox.Text;
     MessageBox.Show(content);
     BarCodeTextBox.Text = "";
     BarCodeTextBox.Focus();
 }
 private void MainWindow_OnLoaded(object sender, RoutedEventArgs e)
 {
     BarCodeTextBox.Focus();
 }
 private void ClearButtonClick(object sender, RoutedEventArgs e)
 {
     BarCodeTextBox.Text = "";
     BarCodeTextBox.Focus();
 }