avalonia/AvaloniaApplication1/Views/AdminPage.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"
             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
             x:Class="AvaloniaApplication1.AdminPage"
			 xmlns:vm="using:AvaloniaApplication1.ViewModels"
			 x:DataType="vm:AdminViewModel">
	<SplitView IsPaneOpen="{Binding Flag}"
           DisplayMode="CompactInline"
			   CompactPaneLength="100"
           OpenPaneLength="300"
			  >
		<SplitView.Pane>
			<StackPanel Orientation="Vertical" HorizontalAlignment="Center" Height="300" VerticalAlignment="Stretch">
				
				<Button Content=">" Command="{Binding Press}"/>
				<ListBox ItemsSource="{Binding Pages}" Width="200" Height="300"	SelectionMode="Single" SelectedItem="{Binding SelectedItem}" IsVisible="{Binding Flag}">
					<ListBox.ItemTemplate>
						<DataTemplate>
							<StackPanel Orientation="Horizontal">
								<TextBlock Text="{Binding }"/>
							</StackPanel>
						</DataTemplate>
					</ListBox.ItemTemplate>
				</ListBox>
			</StackPanel>
		</SplitView.Pane>
		<StackPanel>
			<ContentControl Content="{Binding Page}" Grid.Column="1" Grid.Row="1"/>
		</StackPanel>
	</SplitView>
</UserControl>