docs-desktop/dotnet-desktop-guide/net/wpf/data/snippets/data-binding-overview/csharp/DataValidation.xaml

<Window x:Class="bindings.DataValidation"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        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:local="clr-namespace:bindings"
        xmlns:src="clr-namespace:bindings"
        mc:Ignorable="d"
        Title="DataValidation" Height="450" Width="800">
    <Window.Resources>
        <!-- <ControlTemplate> -->
        <ControlTemplate x:Key="validationTemplate">
            <DockPanel>
                <TextBlock Foreground="Red" FontSize="20">!</TextBlock>
                <AdornedElementPlaceholder/>
            </DockPanel>
        </ControlTemplate>
        <!-- </ControlTemplate> -->
        <!-- <TextBoxStyle> -->
        <Style x:Key="textStyleTextBox" TargetType="TextBox">
            <Setter Property="Foreground" Value="#333333" />
            <Setter Property="MaxLength" Value="40" />
            <Setter Property="Width" Value="392" />
            <Style.Triggers>
                <Trigger Property="Validation.HasError" Value="true">
                    <Setter Property="ToolTip" 
                            Value="{Binding (Validation.Errors).CurrentItem.ErrorContent, RelativeSource={RelativeSource Self}}" />
                </Trigger>
            </Style.Triggers>
        </Style>
        <!-- </TextBoxStyle> -->
        <src:DateConverter x:Key="dateConverter" />
        <src:AuctionItem x:Key="item" />
    </Window.Resources>

    <Grid DataContext="{StaticResource item}">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>

            <ColumnDefinition Width="779*"/>
            <ColumnDefinition Width="21*"/>

        </Grid.ColumnDefinitions>

        <!-- <TextboxStartPrice> -->
        <TextBox Name="StartPriceEntryForm" Grid.Row="2"
                 Style="{StaticResource textStyleTextBox}" Margin="8,5,0,5" Grid.ColumnSpan="2">
            <TextBox.Text>
                <Binding Path="StartPrice" UpdateSourceTrigger="PropertyChanged">
                    <Binding.ValidationRules>
                        <ExceptionValidationRule />
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>
        <!-- </TextboxStartPrice> -->

        <!-- <TextboxStartDate> -->
        <TextBox Name="StartDateEntryForm" Grid.Row="3"
                 Validation.ErrorTemplate="{StaticResource validationTemplate}" 
                 Style="{StaticResource textStyleTextBox}" Margin="8,5,0,5" Grid.ColumnSpan="2">
            <TextBox.Text>
                <Binding Path="StartDate" UpdateSourceTrigger="PropertyChanged" 
                         Converter="{StaticResource dateConverter}" >
                    <Binding.ValidationRules>
                        <src:FutureDateRule />
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>
        <!-- </TextboxStartDate> -->

    </Grid>
</Window>