Avalonia/samples/ControlCatalog/Pages/TabbedPage/TabbedPageDataTemplatePage.xaml

<UserControl xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="ControlCatalog.Pages.TabbedPageDataTemplatePage">
  <DockPanel>
    <ScrollViewer DockPanel.Dock="Right" Width="240">
      <StackPanel Margin="12" Spacing="8">
        <TextBlock Text="Data Templates" FontWeight="SemiBold" FontSize="16"
                   Foreground="{DynamicResource SystemControlHighlightAccentBrush}" />

        <TextBlock FontSize="12" Opacity="0.7" TextWrapping="Wrap"
                   Text="Bind a TabbedPage to a data collection and use PageTemplate to render each item as a ContentPage." />

        <Separator />

        <Button Content="Add Category" Click="OnAddCategory" HorizontalAlignment="Stretch" />
        <Button Content="Remove Last" Click="OnRemoveCategory" HorizontalAlignment="Stretch" />

        <Separator />

        <TextBlock x:Name="StatusText" Text="3 categories" Opacity="0.7" />
      </StackPanel>
    </ScrollViewer>

    <Border DockPanel.Dock="Right" Width="1" Background="{DynamicResource SystemControlForegroundBaseMediumLowBrush}" />

    <Border Margin="12"
            BorderBrush="{DynamicResource SystemControlForegroundBaseMediumLowBrush}"
            BorderThickness="1"
            CornerRadius="6"
            ClipToBounds="True">
      <Panel x:Name="TabbedPageHost" />
    </Border>
  </DockPanel>
</UserControl>