Avalonia/samples/VirtualizationDemo/Views/ExpanderPageView.axaml

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:vm="using:VirtualizationDemo.ViewModels"
             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
             x:Class="VirtualizationDemo.Views.ExpanderPageView"
             x:DataType="vm:ExpanderPageViewModel">
  <ListBox ItemsSource="{Binding Items}">
    <ListBox.ItemTemplate>
      <DataTemplate>
        <Expander Header="{Binding Header}" IsExpanded="{Binding IsExpanded}">
          <Border Width="200" Height="300"/>
        </Expander>
      </DataTemplate>
    </ListBox.ItemTemplate>
  </ListBox>
</UserControl>