IDialogInterfaceOnDismissListener not working

I'm trying to use the IDialogInterfaceOnDismissListener to handle the event when the search bar is closed, however it's not being invoked. I also tried IDialogInterfaceOnCancelListener but it's not being invoked either. What am I missing?

[IntentFilter(new string[]{"android.intent.action.SEARCH"})]
    [MetaData("android.app.searchable", Resource = "@xml/searchable")]
    public class HomeActivity : ActivityBase, INavigationSink, IDialogInterfaceOnDismissListener, IDialogInterfaceOnCancelListener
{
public void OnDismiss(IDialogInterface arg0)
        {
            // TODO: Not called!
        }

        public void OnCancel(IDialogInterface arg0)
        {
            // TODO: Not called!
        }
}