Demo_Validation/MainWindow.axaml

<Window 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="AvaloniaValidationSample.MainWindow"
        x:CompileBindings="False"
        Title="AvaloniaValidationSample">
	<DockPanel>
		<StackPanel Orientation="Horizontal" DockPanel.Dock="Top">
			<Button Content="Add item" Click="AddItem_OnClick"/>
		</StackPanel>
		<ListBox x:Name="ItemsListBox">
			<ListBox.ItemTemplate>
				<DataTemplate>
					<StackPanel>
						<TextBox Text="{Binding Id}"/>
						<TextBox Text="{Binding Password}"/>
						<TextBox Text="{Binding Text}"/>

					</StackPanel>
				</DataTemplate>
			</ListBox.ItemTemplate>
		</ListBox>
	</DockPanel>
</Window>