Can You Do "math" Within WPF Styles That Are Data-bound

- 1 answer

I have a button control style and I want to change the padding from whatever the data-bound version is to adjust for a glyph that needs a 2 pixel offset. I'll use SimpleButton from SimpleStyles.xaml as an example (... shows where the trigger code was removed for conciseness):

<Style x:Key="SimpleButton" TargetType="{x:Type Button}" BasedOn="{x:Null}">
  <Setter Property="FocusVisualStyle" Value="{DynamicResource SimpleButtonFocusVisual}"/>
  <Setter Property="Background" Value="{DynamicResource NormalBrush}"/>
  <Setter Property="BorderBrush" Value="{DynamicResource NormalBorderBrush}"/>
  <Setter Property="Template">
        <ControlTemplate TargetType="{x:Type Button}">
            <!-- We use Grid as a root because it is easy to add more elements to customize the button -->
           <Grid x:Name="Grid">
             <Border x:Name="Border" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}"/>

              <!-- Content Presenter is where the text content etc is placed by the control. The bindings are useful so that the control can be parameterized without editing the template -->
             <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" RecognizesAccessKey="True"/>

What I want to do is add some extra margin where Padding="{TemplateBinding Padding}". Something like Padding="{TemplateBinding Padding} + 2,0,0,0".

Is there a XAML syntax to that? If not, is there a best approach when doing this in code (Decorator?) ?



Currently XAML does not parse expressions in Binding syntax, etc. However, you can use an IValueConverter or IMultiValueConverter to help yourself out:


    <ControlTemplate TargetType="{x:Type Button}">
       <Grid x:Name="Grid">
             <local:ThicknessAdditionConverter x:Key="AdditiveThickness" />
         <Border x:Name="Border">
                 <Binding Path="Padding" RelativeSource="{RelativeSource TemplatedParent}"
                          Converter="{StaticResource AdditiveThickness}">

IValueConverter code behind:

public class ThicknessAdditionConverter : IValueConverter
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        if (value == null) return new Thickness(0, 0, 0, 0);
        if (!(value is Thickness)) throw new ArgumentException("Value not a thickness", "value");
        if (!(parameter is Thickness)) throw new ArgumentException("Parameter not a thickness", "parameter");

        var thickness = new Thickness(0, 0, 0, 0);
        var t1 = (Thickness)value;
        var t2 = (Thickness)parameter;

        thickness.Left = t1.Left + t2.Left;
        thickness.Top = t1.Top + t2.Top;
        thickness.Right = t1.Right + t2.Right;
        thickness.Bottom = t1.Bottom + t2.Bottom;

        return thickness;

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        throw new NotImplementedException();