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" 
                    MinWidth="150"
                    Gap="4">
            <TextBox Watermark="Item Count"
                     UseFloatingWatermark="True"
                     Text="{Binding ItemCount}"/>
            <TextBox Watermark="Extent"
                     UseFloatingWatermark="True"
                     Text="{Binding #listBox.Scroll.Extent, Mode=OneWay}"/>
            <TextBox Watermark="Offset"
                     UseFloatingWatermark="True"
                     Text="{Binding #listBox.Scroll.Offset, Mode=OneWay}"/>
            <TextBox Watermark="Viewport"
                     UseFloatingWatermark="True"
                     Text="{Binding #listBox.Scroll.Viewport, Mode=OneWay}"/>
            <TextBox Watermark="Item to Create"
                     UseFloatingWatermark="True"
                     Text="{Binding NewItemString}"/>
            <Button Command="{Binding AddItemCommand}">Add Item</Button>
            <Button Command="{Binding RemoveItemCommand}">Remove Item</Button>
            <Button Command="{Binding RecreateCommand}">Recreate</Button>
        </StackPanel>

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