remove red rectangle around combobox

Question

i need to remove red rectangle around combobox. I have setup combobox in xaml like (below) this and i`m trying to override of the Validation.ErrorTemplate.

        <ComboBox x:Name="comboPodkategoria" 
                            Margin="0,3,0,0"
                            IsSynchronizedWithCurrentItem="False" 
                            IsEditable="False"
                            ItemsSource="{Binding Source={StaticResource PodKategoriaLookup}, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}"
                            SelectedValue="{Binding IDPodKategoria}"
                            DisplayMemberPath="kat_popis" SelectedValuePath="IDPodkat" TabIndex="5" Style="{StaticResource combostyle}">
                            <Validation.ErrorTemplate>
                                <ControlTemplate>
                                </ControlTemplate>
                            </Validation.ErrorTemplate> 
            </ComboBox>

And style for removing red rectangle, but a have some error in xaml saying that Visibility property is not recognized or is not accessible. Style definition is below.

<Style x:Key="combostyle">
<Style.Triggers>
    <Trigger Property="Validation.HasError" Value="True">
        <Setter Property="Visibility" TargetName="NotValid" Value="Visible"/>
    </Trigger>  
</Style.Triggers>   

Any idea? :(

Answer 1

Use this to modify the Validation.ErrorTemplate

<ControlTemplate x:Key="ComboBoxValidationErrorTemplate">
    <DockPanel>
        <Border BorderBrush="Blue" BorderThickness="4">
            <AdornedElementPlaceholder />
        </Border>
    </DockPanel>
</ControlTemplate>

And then use it in your ComboBox like

<ComboBox Validation.ErrorTemplate="{StaticResource ComboBoxValidationErrorTemplate}"
          ...>

To have no indication of a Validation Error, remove the DockPanel, set Visibility to Collapsed or any other way you like.

Almost forgot, probably the easiest way to remove the "Red Border"

<ComboBox Validation.ErrorTemplate="{x:Null}"
          ...>