WPF One DataTrigger with multiple Values - wpf

Question

I have a Slider and a TextBlock on my WPF window. The TextBlock needs to change the background, foreground and font size by the value of the slider, by rang.
I built a converter that receives the value of the slider and returns a 0, 1 or 3 for each group.
public class ValueByRange : IValueConverter
{
public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
double.TryParse(value?.ToString(), out double dValue);
if (dValue > 80)
return 2;
else if (dValue > 50)
return 1;
return 0;
}
public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
return false;
}
}
My TextBlock looks like this:
<TextBlock Width="30" Text="{Binding ElementName= theSlider, Path=Value}">
<TextBlock.Style>
<Style TargetType="TextBlock">
<Setter Property="Background" Value="Transparent"/>
<Setter Property="Foreground" Value="Black"/>
<Setter Property="FontSize" Value="12"/>
<Setter Property="TextAlignment" Value="Center"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=theSlider, Path=Value, Converter={StaticResource ValueByRange}}" Value="1">
<Setter Property="Background" Value="Yellow"/>
<Setter Property="Foreground" Value="Black"/>
<Setter Property="FontSize" Value="14"/>
</DataTrigger>
<DataTrigger Binding="{Binding ElementName=theSlider, Path=Value, Converter={StaticResource ValueByRange}}" Value="2">
<Setter Property="Background" Value="Red"/>
<Setter Property="Foreground" Value="White"/>
<Setter Property="FontSize" Value="16"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
It's working fine, but it doesn't feel like the best approach. The converter fires 2 time, each for every DataTrigger. I need more than this 3 ranges and that means the converter will fire more times.
It's also not helpful to build a converter for each property, for the same reason.
Is there a way to fire the converter only ones and then check the result (without using code beyond)?
I know this is not the correct syntax, but I mean something like this:
<DataTrigger Binding="{Binding ElementName=theSlider, Path=Value, Converter={StaticResource ValueByRange}}">
<DataTrigger.Value Value ="1">
<Setter Property="Background" Value="Yellow" />
<Setter Property="Foreground" Value="Black" />
<Setter Property="FontSize" Value="14" />
</DataTrigger.Value>
<DataTrigger.Value Value ="2">
<Setter Property="Background" Value="Red" />
<Setter Property="Foreground" Value="White" />
<Setter Property="FontSize" Value="16" />
</DataTrigger.Value>
</DataTrigger>

Answer 1

Well, as Clemens said, there's nothing wrong with having a converter called multiple times.
But if you really want to do it, here's an approach that works:
<Grid>
<Grid.Resources>
<local:ValueByRange x:Key="ValueByRange" />
<Style x:Key="TextBlockInLabelStyle" TargetType="TextBlock">
<Setter Property="Background" Value="Transparent"/>
<Setter Property="Foreground" Value="Black"/>
<Setter Property="FontSize" Value="12"/>
<Setter Property="TextAlignment" Value="Center"/>
<Style.Triggers>
<DataTrigger Binding="{Binding}" Value="1">
<Setter Property="Background" Value="Yellow"/>
<Setter Property="Foreground" Value="Black"/>
<Setter Property="FontSize" Value="14"/>
</DataTrigger>
<DataTrigger Binding="{Binding}" Value="2">
<Setter Property="Background" Value="Red"/>
<Setter Property="Foreground" Value="White"/>
<Setter Property="FontSize" Value="16"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Grid.Resources>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Slider Grid.Row="0"
x:Name="Slider1"
Interval="1"
Minimum="0"
Maximum="100" />
<Slider Grid.Row="1"
x:Name="Slider2"
Interval="1"
Minimum="0"
Maximum="100" />
<Label Grid.Row="2" Content="{Binding ElementName=Slider1, Path=Value, Converter={StaticResource ValueByRange}}">
<Label.Resources>
<Style TargetType="{x:Type TextBlock}" BasedOn="{StaticResource TextBlockInLabelStyle}" />
</Label.Resources>
</Label>
<Label Grid.Row="3" Content="{Binding ElementName=Slider2, Path=Value, Converter={StaticResource ValueByRange}}">
<Label.Resources>
<Style TargetType="{x:Type TextBlock}" BasedOn="{StaticResource TextBlockInLabelStyle}" />
</Label.Resources>
</Label>
</Grid>

Answer 2

I want to make an annotation to the answer above:
This makes use of a very confusing and badly documented feature, which is discussed here and confused the hell out of me when reading the answer.
To be clear: I did NOT understand why the TARGETTYPE here was TextBlock, when we clearly use a Label and the answer is discussed in the link above. It has to do with the fact that the valueconverter returns a DOUBLE, which gets treated with the TEXTBLOCK style while a LABEL style in its place would be ignored. I tested it the hard way...