Preventing a WPF Expander from expanding when header is clicked

Question

How can I prevent a WPF Expander from expanding when its header is clicked? I would like my Expander to expand or collapse only when the expand button itself is clicked.

I imagine the answer has something to do with canceling a bubbled event. If possible I would like to implement the solution in XAML while avoiding retemplating the entire Expander.

Answer 1

There is actually a much simpler XAML solution than modifying templates. Simply DON'T use the Expander's header property in this case. Instead, cover the expander with your own styled TextBlock.

<Application.Resources>
    <Style x:Key="ExpanderHeader" TargetType="{x:Type TextBlock}">
        <Setter Property="Height" Value="22" />
        <Setter Property="Margin" Value="21,0,0,0" />
        <Setter Property="Padding" Value="9,3,0,0" />
        <Setter Property="HorizontalAlignment" Value="Stretch" />
        <Setter Property="VerticalAlignment" Value="Top" />
    </Style>
</Application.Resources>

<Grid>
    <Expander>
        <TextBlock Text="I am some content. I have disowned my default header." Margin="10,5" />
    </Expander>
    <TextBlock Text="I'm filling in for the default header. You'll like me better anyway."
               Style="{StaticResource ResourceKey=ExpanderHeader}"/>
</Grid>