Validations in WPF

Validating textboxes in WPF. The validtion is checked at LostFocus event of TextBox

public void ValidateTextbox(ref TextBox ctrltxt, string p)         {             int count = 0;             string errormessage=string.Empty;             BindingExpression expression = ctrltxt.GetBindingExpression(TextBox.TextProperty);             expression.UpdateSource();             if (true) // check validation condition or reg expression here             {                     ValidationError error = new ValidationError(new ExceptionValidationRule(), expression, errormessage, null);                     Validation.MarkInvalid(expression, error);               }         }

XAML code for the TEXTBOX is as below

<TextBox Name="FieldName" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Text="{Binding Path=DisplayData, ValidatesOnDataErrors=True ,NotifyOnValidationError=True , UpdateSourceTrigger=LostFocus, ValidatesOnExceptions=True}" Grid.Column="1" Margin="4,4,4,4" Validation.ErrorTemplate="{StaticResource InputErrorTemplate}" > </TextBox>

InputErrorTemplate is as below

        <ControlTemplate x:Key="InputErrorTemplate">
            <DockPanel>
                <Border Name="validationBorder" BorderBrush="Red" BorderThickness="2" Padding="1" CornerRadius="3">
                    <Border.Resources>
                        <Storyboard x:Key="_blink">
                            <ColorAnimationUsingKeyFrames AutoReverse="True" BeginTime="00:00:00" Storyboard.TargetName="validationBorder" Storyboard.TargetProperty="(Border.BorderBrush).(SolidColorBrush.Color)" RepeatBehavior="00:00:02">
                                <SplineColorKeyFrame KeyTime="00:00:00.5" Value="#00FF0000"/>
                            </ColorAnimationUsingKeyFrames>
                        </Storyboard>
                    </Border.Resources>
                    <Border.Triggers>
                        <EventTrigger RoutedEvent="FrameworkElement.Loaded">
                            <BeginStoryboard Storyboard="{StaticResource _blink}" />
                        </EventTrigger>
                    </Border.Triggers>
                    <AdornedElementPlaceholder/>
                </Border>
            </DockPanel>
        </ControlTemplate>