wpf targetting version 4.0 from 3.5 affects IDataErrorInfo implementation

Question

I've an MVVM application implementing IDataErrorInfo using version 3.5. I want to try and target 4.0 so have amended the Target Framework setting and changed a few bits around (BitmapFrames and the like). Most things seem just fine and the process was relatively painless, until I noticed that the implentation of IDataErrorInfo has been affected.

My control template for validation looks like this:

    <ControlTemplate x:Key="temp__">
    <Border BorderBrush="Orange" BorderThickness="2" CornerRadius="4" SnapsToDevicePixels="True">    
        <DockPanel>         
        <Image HorizontalAlignment="Left" VerticalAlignment="Center" 
                         Width="16" Height="16" Margin="-20,0,0,0" 
                         Source="{StaticResource ErrorIcon}" 
                         ToolTip="{Binding ElementName=adornedElement, 
                                             Path=AdornedElement.(Validation.Errors), 
                                             Converter={helper:ValidationErrorsToStringConverter}}"/>
        <AdornedElementPlaceholder Name="adornedElement"/>
    </DockPanel>
    </Border>
</ControlTemplate>

and is used in a textbox style like this:

<Setter Property="Validation.ErrorTemplate" Value="{DynamicResource error_holder}">

In my ViewModel, GetValidationError(string propertyName) uses a switch to validate the appropriate property based on my rules.

The issue is that once a validation has been fired it does not update. For instance, a field can be set as required or not. When loaded, the fields that are required are marked as invalid with an appropriate message. Previously, when a value was entered that was still invalid the error message in the tooltip would update. However this no longer works and the error message still remains as a null value message.

Does anyone know of any changes in the implementation of IDataErrorInfo in 4.0 that may account for this? Any idea how to fix it?

Answer 1

Ok, so I've sort of fixed this. Rather than use the default implementation that uses Validation.Errors[0] which gives binding errors when the error is fixed, I'd used a converter. Not sure why this resulted in the behaviour originally described, but it did. So I originally changed back to using Validation.Errors[0] and the error message updated correctly. However, this would result in the binding errors returning. Instead I implemented the advice here prevent binding errors and the issue is resolved.

My ControlTemplate now looks like this:

  <ControlTemplate x:Key="temp__">
<DockPanel LastChildFill="True">
  <Border BorderBrush="Orange" BorderThickness="2" CornerRadius="4" SnapsToDevicePixels="True">
    <Border.Effect>
      <DropShadowEffect ShadowDepth="0" Color="Orange" BlurRadius="10" />
    </Border.Effect>
    <DockPanel>          
      <Image HorizontalAlignment="Left" VerticalAlignment="Center"
                         Width="16" Height="16" Margin="-20,0,0,0" 
                         Source="{DynamicResource ErrorIcon}"               
             ToolTip="{Binding ElementName=adornedElement, 
                               Path=AdornedElement.(Validation.Errors)/ErrorContent}"/>
      <AdornedElementPlaceholder Name="adornedElement"/>
    </DockPanel>        
  </Border>
</DockPanel>

However, where previously a required field was flagged as an error on loading, this no longer happens. The validation only appears once another error has occurred due to user input. How can I fix this?