How can I Set Validation.ErrorTemplate in Code behind?

Question

I've been looking in StackOverflow, and several questions are done. But they don't work.

I have this PasswordBox:

<PasswordBox Width="160"
      HorizontalAlignment="Left"
      Margin="10,3"
      Name="textBoxUserPass"
      local:PasswordBoxAssistant.BindPassword="True"
      local:PasswordBoxAssistant.BoundPassword="{Binding Path=Password, UpdateSourceTrigger=Explicit, 
      ValidatesOnDataErrors=True, ValidatesOnExceptions=True}"
      Validation.ErrorTemplate="{x:Null}" />

I first set the ValidationErrorTemplate="{x:Null}" so first time I load the PasswordBox it doesn't try to validate the box.

When I find a error, I try to change the Validation.ErrorTemplate so it shows a red border (as the ErrorTemplate I have defined) like this:

BindingExpression bePassword = textBoxUserPass.GetBindingExpression(PasswordBoxAssistant.BoundPassword);
if (bePassword != null)
{
    bePassword.UpdateSource();
    if (bePassword.HasError)
    {
        var validationError = new ValidationError(new ExceptionValidationRule(), bePassword);
        Validation.MarkInvalid(bePassword, validationError);
        validationError.ErrorContent = Cultures.Resources.MessageNoPassword;
        var b = Resources["validationTemplate"] as ControlTemplate;
        Validation.SetErrorTemplate(textBoxUserPass, b);
        }
    }
}

Where I have defined my validationTemplate on a ResourceDictionary.xaml like this:

    <Style x:Key="validationTemplate" TargetType="{x:Type TextBox}">
    <Setter Property="Validation.ErrorTemplate">
        <Setter.Value>
            <ControlTemplate>
                <DockPanel LastChildFill="True">
                    <TextBlock DockPanel.Dock="Right" 
                    Foreground="Red"
                    FontSize="12pt">
                    *
                    </TextBlock>
                    <Border BorderBrush="Red" BorderThickness="1" CornerRadius="5">
                        <AdornedElementPlaceholder />
                    </Border>
                </DockPanel>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

A regular box, as you can see.

My problem comes when trying to find this resource to change my Validation.ErrorTemplate in code behind. I put a breakpoint, and this line:

var b = FindResource("validationTemplate") as ControlTemplate;

says that b is null. How I can find "validationTemplate" and use it??

Answer 1

Your validationTemplate is a Style with a Template. Try Template only instead:

<ControlTemplate x:Key="validationTemplate">
    <DockPanel LastChildFill="True">
        <TextBlock DockPanel.Dock="Right" 
        Foreground="Red"
        FontSize="12pt">
        *
        </TextBlock>
        <Border BorderBrush="Red" BorderThickness="1" CornerRadius="5">
            <AdornedElementPlaceholder />
        </Border>
    </DockPanel>
</ControlTemplate>