How do you programmatically set focus to the SelectedItem in a WPF ListBox that already has focus?

It's a couple lines of code. If you didn't want it in code-behind, I sure it could be packaged in a attached behaviour.

private void Button_Click(object sender, RoutedEventArgs e){    MainListBox.SelectedItem = MainListBox.Items[3];    MainListBox.UpdateLayout(); // Pre-generates item containers     var listBoxItem = (ListBoxItem) MainListBox        .ItemContainerGenerator        .ContainerFromItem(MainListBox.SelectedItem);    listBoxItem.Focus();}

Maybe with an attached behavior? Something like

public static DependencyProperty FocusWhenSelectedProperty = DependencyProperty.RegisterAttached(            "FocusWhenSelected",             typeof(bool),             typeof(FocusWhenSelectedBehavior),             new PropertyMetadata(false, new PropertyChangedCallback(OnFocusWhenSelectedChanged)));private static void OnFocusWhenSelectedChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)    {        var i = (ListBoxItem)obj;        if ((bool)args.NewValue)           i.Selected += i_Selected;        else           i.Selected -= i_Selected;    }static void i_Selected(object sender, RoutedEventArgs e){    ((ListBoxItem)sender).Focus();}

and in xaml

       <Style TargetType="ListBoxItem">            <Setter Property="local:FocusWhenSelectedBehavior.FocusWhenSelected" Value="True"/>        </Style>

You need only use ListBox.SelectedItem and then use ListBox.ScrollIntoView(listBox.SelectedItem)

Example code:

        private void textBox2_TextChanged(object sender, TextChangedEventArgs e)    {        var comparision = StringComparison.InvariantCultureIgnoreCase;        string myString = textBox2.Text;        List<dynamic> index = listBox.Items.SourceCollection.OfType<dynamic>().Where(x=>x.Nombre.StartsWith(myString,comparision)).ToList();        if (index.Count > 0) {         listBox.SelectedItem= index.First();            listBox.ScrollIntoView(listBox.SelectedItem);        }    }