WPF Combobox Validation.ErrorTemplate error - wpf

Question

I have a combobox that i need to edit its error template to show a red border when there is a validation error.
I am using the following style
<Style TargetType="{x:Type ComboBox}" >
<Setter Property="Validation.ErrorTemplate">
<Setter.Value>
<ControlTemplate>
<DockPanel>
<Border BorderBrush="Red" BorderThickness="3">
<AdornedElementPlaceholder />
</Border>
</DockPanel>
</ControlTemplate>
</Setter.Value>
</Setter>
<Setter Property="FontFamily" Value="Segoe UI" />
<Setter Property="FontSize" Value="12" />
<Setter Property="VerticalAlignment" Value="Center" />
</Style>
The border never shows up when validation errors occur. Any tips what is going wrong?

Answer 1

The Style you posted works. You should check your binding, did you add ValidatesOnDataErrors=True and ValidatesOnExceptions=True to the binding of SelectedValue?

Answer 2

enter code heretry without the dock panel, that is uneuseful since it wraps jus one element. However, sicnecerely I don't wnow if it makes sense to wrap a textbox with a border, since it has already a border! You should try to change directly the colour of its border. You could try to use again the panel but then put the border around the panel ie:
Border BorderBrush="Red" BorderThickness="3"
DockPanel
AdornedElement
This makes more sense because the wrap panel has not its own border.

Answer 3

Use This.
<Style x:Key="textBoxStyle" TargetType="{x:Type telerik:RadMaskedTextBox}">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="True">
<Setter Property="ToolTip" Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors)[0].ErrorContent}"/>
<Setter Property="Control.BorderBrush" Value="Red" />
</Trigger>
</Style.Triggers>
</Style>

Answer 4

I don't like any of the responses here. Simply put, how do you change the border color for the error template for a ComboBox using Blend or not? It shouldn't be acceptable to draw another border around the existing border of the ComboBox. I've figured out how to creat a ControlTemplate in Blend but not a Validation Template.
I've come close with trying to make it appear like I've changed the actual border color, but that's not what I actually want. Suggestions? To complicate it a bit, I'd like to display a red asterisk outside of the right border of the control.
The following code is a close attempt, but it is actually drawing a border inside the ComboBox and if you look close, you can see that the border is 2 pixels wide when combined with the ComboBox border:
<DockPanel Name="myDockPanel">
<AdornedElementPlaceholder>
<Border BorderBrush="Blue" BorderThickness="1" CornerRadius="2" />
</AdornedElementPlaceholder>
<TextBlock Text="*" FontWeight="Bold" FontSize="14" Foreground="Red" DockPanel.Dock="Left" ToolTip="{Binding .CurrentItem}" />
</DockPanel>

Answer 5

I searched around some more and came up with a solution based on another article here: WPF - How to apply style to AdornedElementPlaceholder's AdornedElement?
<!-- This works -->
<ComboBox Name="comboBox1" Style="{StaticResource NewComboBoxStyle}" Validation.ErrorTemplate="{StaticResource comboBoxValidationTemplate}" />
<SolidColorBrush x:Key="MainBorderBrush">#FF91B3FF</SolidColorBrush>
<Style x:Key="NewComboBoxStyle" TargetType="{x:Type ComboBox}" BasedOn="{StaticResource myErrorTemplate}">
<Setter Property="BorderBrush" Value="{DynamicResource MainBorderBrush}" />
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="True">
<Setter Property="BorderBrush" Value="Blue" />
</Trigger>
</Style.Triggers>
</Style>
<!-- Sets ToolTip when Validation.HasError is True. -->
<Style TargetType="Control" x:Key="myErrorTemplate">
<Style.Triggers>
<Trigger Property="Validation.HasError" Value="true">
<Setter Property="ToolTip"
Value="{Binding RelativeSource={x:Static RelativeSource.Self},
Path=(Validation.Errors).CurrentItem.ErrorContent}"/>
</Trigger>
</Style.Triggers>
</Style>
<ControlTemplate x:Key="comboBoxValidationTemplate">
<DockPanel Name="myDockPanel">
<AdornedElementPlaceholder/>
<TextBlock Text="*" FontWeight="Bold" FontSize="14" Foreground="Red" DockPanel.Dock="Left" ToolTip="{Binding .CurrentItem}" />
</DockPanel>
</ControlTemplate>