private void CBOperation_DropDownClosed(object sender, EventArgs e)
        {
            if (CBOperation.SelectedIndex == 0)
            {
                EFromSystemNumber2.Visibility = Visibility.Hidden;
                CBFromSystem2.Visibility      = Visibility.Hidden;

                EFromSystemNumber2.Text     = "";
                CBFromSystem2.SelectedIndex = CBFromSystem1.SelectedIndex;
            }
            else
            {
                EFromSystemNumber2.Visibility = Visibility.Visible;
                CBFromSystem2.Visibility      = Visibility.Visible;
            }

            ESystemNumber_TextChanged(sender, null);

            if (CBOperation.SelectedIndex == 6)
            {
                CBFromSystem2.IsEnabled     = false;
                CBFromSystem2.SelectedIndex = 8;
            }
            else
            {
                CBFromSystem2.IsEnabled = true;
            }

            EFromSystemNumber1.Focus();
        }
 private void MainWindow1_Initialized(object sender, EventArgs e)
 {
     CBOperation_DropDownClosed(sender, null);
     EFromSystemNumber1.Focus();
 }