/// <summary>
 /// Method called when the 'OK' button is clicked.
 /// </summary>
 /// <param name="sender">Sender.</param>
 /// <param name="e">Event args.</param>
 private void OkClicked(object sender, EventArgs e)
 {
     // Save the DRM username and password in the preferences.
     AppPreferences.SetDRMUsername(usernameEntry.Text);
     AppPreferences.SetDRMPassword(passwordEntry.Text);
     AppPreferences.SetDRMServer(serverPicker.SelectedIndex == 0 ? SERVER_PRODUCTION : SERVER_TEST);
     ClosePopup();
 }