Avalonia/samples/VirtualizationDemo/MainWindow.xaml

<Window xmlns="https://github.com/avaloniaui"
        Title="AvaloniaUI Virtualization Test"
        Width="800"
        Height="600">
    <DockPanel LastChildFill="True" Margin="16">
        <StackPanel DockPanel.Dock="Right" 
                    Margin="16 0 0 0" 
                    MinWidth="150"
                    Gap="4">
            <DropDown Items="{Binding VirtualizationModes}"
                      SelectedItem="{Binding VirtualizationMode}"/>
            <DropDown Items="{Binding Orientations}"
                      SelectedItem="{Binding Orientation}"/>
            <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}"/>
            <TextBlock>Horiz. ScrollBar</TextBlock>
            <DropDown Items="{Binding ScrollBarVisibilities}"
                      SelectedItem="{Binding HorizontalScrollBarVisibility}"/>
            <TextBlock>Vert. ScrollBar</TextBlock>
            <DropDown Items="{Binding ScrollBarVisibilities}"
                      SelectedItem="{Binding VerticalScrollBarVisibility}"/>
            <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>
            <Button Command="{Binding SelectFirstCommand}">Select First</Button>
            <Button Command="{Binding SelectLastCommand}">Select Last</Button>
        </StackPanel>

        <ListBox Name="listBox" 
                 Items="{Binding Items}" 
                 SelectedItems="{Binding SelectedItems}"
                 ScrollViewer.HorizontalScrollBarVisibility="{Binding HorizontalScrollBarVisibility, Mode=TwoWay}"
                 ScrollViewer.VerticalScrollBarVisibility="{Binding VerticalScrollBarVisibility, Mode=TwoWay}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <Expander ExpandDirection="Down">
                            <StackPanel Background="#FFFEFEFE">
                                <Panel Background="Red" Height="200" Width="200" />
                            </StackPanel>
                        </Expander>
                        <Grid ColumnDefinitions="400, *, 100" Margin="30 0 0 0">
                            <TextBlock Text="{Binding Header}" />
                        </Grid>
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </DockPanel>
</Window>