protected override void OnListBoxDetached()
{
base.OnListBoxDetached();
Extender.Dispose();
Extender = null;
_extender.Dispose();
_extender = null;
}
protected override void OnListBoxAttached()
{
base.OnListBoxAttached();
_extender = new UserColumnExtender(this);
Extender = new Popup(_extender);
}