How to dynamically change Validation.ErrorTemplate based on the ErrorContent in xaml

I am trying to implement what is described in this answer. I would like to have one template for validation warnings and one for errors. I thought I had it figured out by binding to Validation.ErrorTemplate in a style trigger like this:

<Style TargetType="TextBox">
        <Style.Triggers>
            <Trigger Property="Validation.HasError" Value="true">
                <Setter Property="Validation.ErrorTemplate" Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Converter={StaticResource ValidationTemplateConverter}, Path=(Validation.Errors)[0].ErrorContent}" ></Setter>
            </Trigger>
        </Style.Triggers>
    </Style>

The converter simply takes a key from the ErrorContent and does a lookup in a ResourceDictionary for the correct template. Unfortunately开发者_运维百科 this doesn't work because binding to Validation.ErrorTemplate is not allowed -- ArgumentException

'ErrorTemplate' property cannot be data-bound.
Parameter name: dp

Anybody else try to implement something like this?

Couldn't you move this logic into a DataTemplateSelector? I'm assuming you're binding Validation.Errors to some sort of ItemsControl -- that ItemsControl can have a DataTemplateSelector that displays the error content differently depending on if it is a warning or an error.

If you're only showing the first error then you could always have your template include a ContentControl, DataBind the Content to Validation.Errors[0] and apply a ContentTemplateSelector

<Style TargetType="TextBox">
      <Setter Property="Validation.ErrorTemplate">
            <Setter.Value>
                <ControlTemplate>
                    <DockPanel>
                        <ItemsControl ItemsSource="{Binding RelativeSource={RelativeSource TemplatedParent},  Path=(Validation.Errors)"
                                 ItemTemplateSelector="{StaticResource ErrorTemplateSelector}" />
                        <AdornedElementPlaceholder/>
                    </DockPanel>
                </ControlTemplate>
            </Setter.Value>
      </Setter>
</Style>