Changing the text style of a WPF GroupBox header

I wanted to change the style of the header of a WPF GroupBox today and had to do a little digging to figure out how to do it.

The GroupBox header is not limited to just text - it can be any control. Because of this, no header text styling options are available directly as properties of the GroupBox control. Instead, you need to modify the DataTemplate of the GroupBox header.

Here is a style that will make the GroupBox header text black and bold:

<Style x:Key="MyGroupBoxStyle" TargetType="{x:Type GroupBox}">
 <Setter Property="HeaderTemplate">
   <Setter.Value>
     <DataTemplate>
       <TextBlock Text="{Binding}" Foreground="Black" FontWeight="Bold"/>
     </DataTemplate>
   </Setter.Value>
 </Setter>
</Style>

Note that this method is a bit of a hack, in that it assumes that your header is text. If it isn't, though, you've added your own custom controls to the header and you don't have a styling problem in the first place...