Validating textboxes in WPF. The validtion is checked at LostFocus event of TextBox
  1. public void ValidateTextbox(ref TextBox ctrltxt, string p)
  2. {
  3. int count = 0;
  4. string errormessage=string.Empty;
  5. BindingExpression expression = ctrltxt.GetBindingExpression(TextBox.TextProperty);
  6. expression.UpdateSource();
  7. if (true) // check validation condition or reg expression here
  8. {
  9. ValidationError error = new ValidationError(new ExceptionValidationRule(), expression, errormessage, null);
  10. Validation.MarkInvalid(expression, error);
  12. }
  14. }


XAML code for the TEXTBOX is as below

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

InputErrorTemplate is as below
  1. <ControlTemplate x:Key="InputErrorTemplate">  
  2.     <DockPanel>  
  3.         <Border Name="validationBorder" BorderBrush="Red" BorderThickness="2" Padding="1" CornerRadius="3">  
  4.             <Border.Resources>  
  5.                 <Storyboard x:Key="_blink">  
  6.                     <ColorAnimationUsingKeyFrames AutoReverse="True" BeginTime="00:00:00" Storyboard.TargetName="validationBorder" Storyboard.TargetProperty="(Border.BorderBrush).(SolidColorBrush.Color)" RepeatBehavior="00:00:02">  
  7.                         <SplineColorKeyFrame KeyTime="00:00:00.5" Value="#00FF0000"/>  
  8.                     </ColorAnimationUsingKeyFrames>  
  9.                 </Storyboard>  
  10.             </Border.Resources>  
  11.             <Border.Triggers>  
  12.                 <EventTrigger RoutedEvent="FrameworkElement.Loaded">  
  13.                     <BeginStoryboard Storyboard="{StaticResource _blink}" />  
  14.                 </EventTrigger>  
  15.             </Border.Triggers>  
  16.             <AdornedElementPlaceholder/>  
  17.         </Border>  
  18.     </DockPanel>  
  19. </ControlTemplate>