Avalonia/samples/VirtualizationTest/MainWindow.xaml

<Window xmlns="https://github.com/avaloniaui"
        Title="Avalonia Virtualization Test">
    <DockPanel LastChildFill="True" Margin="16">
        <StackPanel DockPanel.Dock="Right" Margin="16 0 0 0">
            <TextBox Watermark="Item Count"
                     UseFloatingWatermark="True"
                     Text="{Binding ItemCount}"/>
        </StackPanel>

        <ListBox Items="{Binding Items}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Header}"/>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </DockPanel>
</Window>