WPF override property specified on element from style trigger - wpf

Question

I have two TextBlock Run elements with different colors (one is explicitly set on the element). I want them both to change color to red when the value Foo is zero, using the same style. Is this possible somehow? I would rather not duplicate the Style. This is what I want to work:
<Style x:Key="ForegroundStyleTrigger" TargetType="Run">
<Style.Triggers>
<DataTrigger Binding="{Binding Foo}" Value="0">
<Setter Property="Foreground" Value="{StaticResource RedBrush}"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
<TextBlock>
<Run Text="{Binding Foo, Mode=OneWay}"
Style="{StaticResource ForegroundStyleTrigger}"/>
<Run Text="{Binding Bar, Mode=OneWay}"
Foreground="Blue"
Style="{StaticResource ForegroundStyleTrigger}"/>
</TextBlock>
But since the locally defined color (the one defined on the element) takes precedence over style triggers, nothing happens and the text stays blue for that text run.
Question: Can I override a TextBlocks runs color from a style resource?
If not, how can achieve the expected result without duplicating the style resource?

Answer 1

Can I override a TextBlocks runs color from a style resource?
No, you cannot override a local value using a style setter.
If not, how can achieve the expected result without duplicating the style resource?
If you want the Foreground of the second Run element to be Blue by default and Red only if the Foo source property returns "0" you could create another style and base this one on your existing one:
<Style x:Key="ForegroundStyleTrigger" TargetType="Run">
<Style.Triggers>
<DataTrigger Binding="{Binding Foo}" Value="0">
<Setter Property="Foreground" Value="Red"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
<Style x:Key="BlueByDefault" BasedOn="{StaticResource ForegroundStyleTrigger}" TargetType="Run">
<Setter Property="Foreground" Value="Blue" />
</Style>
<TextBlock>
<Run Text="{Binding Foo, Mode=OneWay}" Style="{StaticResource ForegroundStyleTrigger}"/>
<Run Text="{Binding Bar, Mode=OneWay}" Style="{StaticResource BlueByDefault}"/>
</TextBlock>
But you cannot set the Foreground property to a local value if you want your style setters to apply.

Answer 2

You would use Style inheritance to achieve what you're asking. The trick then is that all properties must be in the Style as local explicitly set values override implicitly set Style values:
<Style x:Key="ForegroundStyleTrigger" TargetType="Run">
<Style.Triggers>
<DataTrigger Binding="{Binding Foo}" Value="0">
<Setter Property="Foreground" Value="{StaticResource RedBrush}"></Setter>
</DataTrigger>
</Style.Triggers>
</Style>
<Style x:Key="BlueForegroundStyleTrigger" BasedOn="{StaticResource ForegroundStyleTrigger}" TargetType="Run">
<Setter Property="Foreground" Value="Blue"/>
</Style>
<TextBlock>
<Run Text="{Binding Foo, Mode=OneWay}"
Style="{StaticResource ForegroundStyleTrigger}"/>
<Run Text="{Binding Bar, Mode=OneWay}"
Style="{StaticResource BlueForegroundStyleTrigger}"/>
</TextBlock>