/// <summary>
/// 切换扫描仪选择时，关闭之前选择的扫描仪。
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void DataSrc_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (twSession.State >= TwState.OpenDS)
{
twSession.CloseDS();
}
}