Underline Label in WPF, using styles

Question

I have the following style:

<Style x:Key="ActionLabelStyle" TargetType="{x:Type Label}">
    <Setter Property="Margin" Value="10,3" />
    <Setter Property="Padding" Value="0" />
    <Setter Property="TextBlock.TextWrapping" Value="Wrap" />
    <Setter Property="FontFamily" Value="Calibri" />
    <Style.Triggers>
        <MultiTrigger>
            <MultiTrigger.Conditions>
                <Condition Property="IsMouseOver" Value="True" />
                <Condition Property="IsEnabled" Value="True" />
            </MultiTrigger.Conditions>
            <Setter Property="Background" Value="Red" />
            <Setter Property="TextBlock.TextDecorations" Value="Underline" />
        </MultiTrigger>
    </Style.Triggers>
</Style>

So basically, I want to have a label which is underlined when it is enabled and the mouse cursor is over it. The part of this style which is not working is the <Setter Property="TextBlock.TextDecorations" Value="Underline" />. Now, what am I doing wrong here? Thanks for all the help.

Answer 1

This is actually much more difficult than it appears. In WPF, a Label is not a TextBlock. It derives from ContentControl and can therefore host other, non-text controls in its Content collection.

However, you can specify a string as the content as in the example below. Internally, a TextBlock will be constructed to host the text for you.

<Label Content="Test!"/>

This internally translates to:

    <Label>
        <Label.Content>
            <TextBlock>
                Test!
            </TextBlock>
        </Label.Content>
    </Label>

The simple solution to this would be for the TextDecorations property of a TextBlock to be an attached property. For example, FontSize is designed this way, so the following works:

    <Label TextBlock.FontSize="24">
        <Label.Content>
            <TextBlock>
                Test!
            </TextBlock>
        </Label.Content>
    </Label>

The TextBlock.FontSize attached property can be applied anywhere in the visual tree and will override the default value for that property on any TextBlock descendant in the tree. However, the TextDecorations property is not designed this way.

This leaves you with at least a few options.

1. Use color, border, cursor, etc., instead of underlined text because this is 100% easier to implement.
2. Change the way you are doing this to apply the Style to the TextBlock instead.
3. Go to the trouble to create your own attached property and the control template to respect it.
4. Do something like the following to nest the style for TextBlocks that appear as children of your style:

FYI, this is the ugliest thing I've done in WPF so far, but it works!

    <Style x:Key="ActionLabelStyle" TargetType="{x:Type Label}">
        <Setter Property="Margin" Value="10,3" />
        <Setter Property="Padding" Value="0" />
        <Setter Property="TextBlock.TextWrapping" Value="Wrap" />
        <Setter Property="FontFamily" Value="Calibri" />
        <Style.Triggers>
            <MultiTrigger>
                <MultiTrigger.Conditions>
                    <Condition Property="IsMouseOver" Value="True" />
                    <Condition Property="IsEnabled" Value="True" />
                </MultiTrigger.Conditions>
                <Setter Property="Background" Value="Red" />
            </MultiTrigger>
        </Style.Triggers>
        <Style.Resources>
            <Style TargetType="TextBlock">
                <Style.Triggers>
                    <MultiDataTrigger>
                        <MultiDataTrigger.Conditions>
                            <Condition Binding="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=Label}, Path=IsMouseOver}" Value="True" />
                            <Condition Binding="{Binding RelativeSource={RelativeSource Self}, Path=IsEnabled}" Value="True" />
                        </MultiDataTrigger.Conditions>
                        <Setter Property="TextDecorations" Value="Underline"/>
                    </MultiDataTrigger>
                </Style.Triggers>
            </Style>
        </Style.Resources>
    </Style>

This works because it is overriding the default style of any TextBlock beneath a Label of this style. It then uses a MultiDataTrigger to allow relative binding back up to the Label to check if its IsMouseOver property is True. Yuck.

Edit:

Note that this only works if you explicitly create the TextBlock. I was incorrect when I posted this because I had already dirtied up my test Label. Boo. Thanks, Anvaka, for pointing this out.

    <Label Style="{StaticResource ActionLabelStyle}">
        <TextBlock>Test!</TextBlock>
    </Label>

This works, but if you have to go to this trouble, you're just working too hard. Either someone will post something more clever, or as you said, my option 1 is looking pretty good right now.

Answer 2

Further to Jerry's answer, in order to avoid having to add the TextBlock into the template each time you can let the style do this too by adding the Setter property into the style:

<Setter Property="Template">
    <Setter.Value>
        <ControlTemplate TargetType="{x:Type Label}">
            <TextBlock>
                <ContentPresenter />
            </TextBlock>
        </ControlTemplate>
    </Setter.Value>
</Setter>

Then your Label is back to:

<Label Content="Test!" Style="{StaticResource ActionLabelStyle}" />

Thanks Jerry!

Andrew.

Answer 3

I think the issue is that TextBlock.TextDecorations is not defined on Label.

You can use this approach if you're happy to use a TextBlock rather than a Label.