Validations in WPF

Validating dynamically in WPF using patterns like MVVM.

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>