CODEWITHSUNDEEP
c#wpfvalidationhide
Kevin Cruijssen
Kevin Cruijssen

Reputation: 9326

Hide ValidationError border & text on view with a custom Style

In our project we have a LookUp Base ViewModel which has a Required-Attribute on the SelectedItem property. I have another View that uses one of the child LookUps, which should ignore the Required-attribute. I've already overridden the IsValid method in the ViewModel, so saving without caring about the Required works correctly, but unfortunately it's still showing the validation error on the view when I empty the LookUp: enter image description here

I had a couple of possibilities:

  1. Split the LookUpBaseViewModel into two childs that are also "BaseViewModels", one with the RequiredAttribute and one without. This works, but it seems like a bit too much work and a lot of extra classes for just a single view that doesn't need to show the validation errors on the View.

  2. Replace the RequiredAttribute with a RequiredIf-Attribute and add a boolean IsRequired parameter to the Constructor. This doesn't work since we use AutoFac in our project, so we can't use a boolean parameter for the ILookUpBaseViewModel-interface implementation.

  3. Add a style to the LookUp-ContentControl in the View to hide the ValidationError border & text. This seemed like the easiest solution on paper, and it also makes sense to just hide the unwanted ValidationError border & text.

So, my question, how do I make the style to hide the default WPF validation error (so the red border and the text behind it)? I'm a novice when it comes to styles, but this is what I've tried (and which doesn't do anything it seems):

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Style x:Key="HideValidationErrorContentControlStyle" TargetType="{x:Type ContentControl}" BasedOn="{StaticResource {x:Type ContentControl}}">
        <Setter Property="Validation.ErrorTemplate">
            <Setter.Value>
                <ControlTemplate>
                    <!-- Empty -->
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Style.Triggers>
            <Trigger Property="Validation.HasError" Value="True">
                <Setter Property="Validation.ErrorTemplate">
                    <Setter.Value>
                        <ControlTemplate>
                            <!-- Empty -->
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Trigger>
        </Style.Triggers>
    </Style>

</ResourceDictionary>

With the style on my LookUp-ContentControl like this:

<ContentControl x:Name="MyLookup" Style="{StaticResource HideValidationErrorContentControlStyle}"/>

This is the result I want (even when a ValidationError would normally be shown): enter image description here

Upvotes: 2

Views: 438

Answers (1)

almulo
almulo

Reputation: 4978

Maybe it isn't your LookUp-ContentControl the one showing the error, but another control inside it. A TextBox, maybe?

Also, instead of leaving the ErrorTemplate empty, try to add an AdornedElementPlaceholder.

<Style x:Key="HideValidationErrorContentControlStyle" TargetType="{x:Type ContentControl}" BasedOn="{StaticResource {x:Type ContentControl}}">
    <Setter Property="Validation.ErrorTemplate">
        <Setter.Value>
            <ControlTemplate>
                <AdornedElementPlaceholder />
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

It's likely this isn't needed, but better be safe than sorry.

Upvotes: 1

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