May this will help you.
private void listBox1_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if(listBox1.SelectedIndex==-1)
return;
if (listBox1.SelectedItem == null)
return;
LIST data = (sender as ListBox).SelectedItem as LIST;
string result = data.item.ToString();
listBox1.SelectedIndex = -1;
}