Preventing a WPF Expander from expanding when header is clicked
The header is the button that creates the event, so you need to change the template for your Expander to just have the expander icon as the button.
Here is a post of how to change the expander.
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>
I modified the default template for the Expander control as suggested by Simeon.
The following ControlTemplate defines an expander, which only reacts (expands/collapses) when the user clicks on the header icon.
This is quick and dirty so expect it to break.
<ControlTemplate x:Key="LazyExpanderTemplate" TargetType="Expander">
<Border BorderThickness="{TemplateBinding Border.BorderThickness}" CornerRadius="3,3,3,3" BorderBrush="{TemplateBinding Border.BorderBrush}" Background="{TemplateBinding Panel.Background}" SnapsToDevicePixels="True">
<DockPanel>
<DockPanel DockPanel.Dock="Top" Name="HeaderSite">
<ToggleButton
DockPanel.Dock="Left"
IsChecked="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=IsExpanded}"
Foreground="{TemplateBinding TextElement.Foreground}"
FontFamily="{TemplateBinding TextElement.FontFamily}"
FontSize="{TemplateBinding TextElement.FontSize}"
FontStretch="{TemplateBinding TextElement.FontStretch}"
FontStyle="{TemplateBinding TextElement.FontStyle}"
FontWeight="{TemplateBinding TextElement.FontWeight}"
HorizontalContentAlignment="{TemplateBinding Control.HorizontalContentAlignment}"
VerticalContentAlignment="{TemplateBinding Control.VerticalContentAlignment}"
Padding="{TemplateBinding Control.Padding}"
MinWidth="0"
MinHeight="0"
Margin="1,1,1,1"
>
<ToggleButton.Style>
<Style TargetType="ToggleButton">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Border Padding="{TemplateBinding Control.Padding}">
<Grid Background="#00FFFFFF" SnapsToDevicePixels="False">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="19" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Ellipse Stroke="#FFA9A9A9" Name="circle" Width="19" Height="19" HorizontalAlignment="Center" VerticalAlignment="Center" />
<Ellipse Name="shadow" Width="17" Height="17" HorizontalAlignment="Center" VerticalAlignment="Center" Visibility="Hidden" />
<Path Data="M1,1.5L4.5,5 8,1.5" Stroke="#FF666666" StrokeThickness="2" Name="arrow" HorizontalAlignment="Center" VerticalAlignment="Center" SnapsToDevicePixels="False" />
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsChecked" Value="True" >
<Setter Property="Path.Data" TargetName="arrow">
<Setter.Value>
<StreamGeometry>M1,4.5L4.5,1 8,4.5</StreamGeometry>
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="UIElement.IsMouseOver" Value="True">
<Setter Property="Shape.Stroke" TargetName="circle">
<Setter.Value>
<SolidColorBrush>#FF666666</SolidColorBrush>
</Setter.Value>
</Setter>
<Setter Property="Shape.Stroke" TargetName="arrow">
<Setter.Value>
<SolidColorBrush>#FF222222</SolidColorBrush>
</Setter.Value>
</Setter>
<Setter Property="UIElement.Visibility" TargetName="shadow">
<Setter.Value>
<x:Static Member="Visibility.Visible" />
</Setter.Value>
</Setter>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ToggleButton.Style>
<ToggleButton.FocusVisualStyle>
<Style TargetType="IFrameworkInputElement">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Border>
<Rectangle Stroke="#FF000000" StrokeThickness="1" StrokeDashArray="1 2" Margin="0,0,0,0" SnapsToDevicePixels="True" />
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</ToggleButton.FocusVisualStyle>
</ToggleButton>
<ContentPresenter
RecognizesAccessKey="True"
Content="{TemplateBinding HeaderedContentControl.Header}"
ContentTemplate="{TemplateBinding HeaderedContentControl.HeaderTemplate}"
ContentStringFormat="{TemplateBinding HeaderedContentControl.HeaderStringFormat}"
Margin="4,0,0,0"
HorizontalAlignment="Left"
VerticalAlignment="Center"
SnapsToDevicePixels="True"
/>
</DockPanel>
<ContentPresenter Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Name="ExpandSite" Margin="{TemplateBinding Control.Padding}" HorizontalAlignment="{TemplateBinding Control.HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding Control.VerticalContentAlignment}" Visibility="Collapsed" Focusable="False" DockPanel.Dock="Bottom" />
</DockPanel>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="Expander.IsExpanded">
<Setter Property="UIElement.Visibility" TargetName="ExpandSite">
<Setter.Value>
<x:Static Member="Visibility.Visible" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
<Trigger Property="Expander.ExpandDirection" Value="Right">
<Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Right"/>
<Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Left"/>
<Setter Property="FrameworkElement.Style" TargetName="HeaderSite">
<Setter.Value>
<Style TargetType="ToggleButton">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Border Padding="{TemplateBinding Control.Padding}">
<Grid Background="#00FFFFFF" SnapsToDevicePixels="False">
<Grid.RowDefinitions>
<RowDefinition Height="19" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid>
<Grid.LayoutTransform>
<TransformGroup>
<TransformGroup.Children>
<RotateTransform Angle="-90" />
</TransformGroup.Children>
</TransformGroup>
</Grid.LayoutTransform>
<Ellipse Stroke="#FFA9A9A9" Name="circle" Width="19" Height="19" HorizontalAlignment="Center" VerticalAlignment="Center" />
<Ellipse Name="shadow" Width="17" Height="17" HorizontalAlignment="Center" VerticalAlignment="Center" Visibility="Hidden" />
<Path Data="M1,1.5L4.5,5 8,1.5" Stroke="#FF666666" StrokeThickness="2" Name="arrow" HorizontalAlignment="Center" VerticalAlignment="Center" SnapsToDevicePixels="False" />
</Grid>
<ContentPresenter RecognizesAccessKey="True" Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Margin="0,4,0,0" HorizontalAlignment="Center" VerticalAlignment="Top" SnapsToDevicePixels="True" Grid.Row="1" />
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsChecked">
<Setter Property="Path.Data" TargetName="arrow">
<Setter.Value>
<StreamGeometry>M1,4.5L4.5,1 8,4.5</StreamGeometry>
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
<Trigger Property="UIElement.IsMouseOver">
<Setter Property="Shape.Stroke" TargetName="circle">
<Setter.Value>
<SolidColorBrush>#FF666666</SolidColorBrush>
</Setter.Value>
</Setter>
<Setter Property="Shape.Stroke" TargetName="arrow">
<Setter.Value>
<SolidColorBrush>#FF222222</SolidColorBrush>
</Setter.Value>
</Setter>
<Setter Property="UIElement.Visibility" TargetName="shadow">
<Setter.Value>
<x:Static Member="Visibility.Visible" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
</Trigger>
<Trigger Property="Expander.ExpandDirection">
<Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Top"/>
<Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Bottom"/>
<Setter Property="FrameworkElement.Style" TargetName="HeaderSite">
<Setter.Value>
<Style TargetType="ToggleButton">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Border Padding="{TemplateBinding Control.Padding}">
<Grid Background="#00FFFFFF" SnapsToDevicePixels="False">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="19" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid>
<Grid.LayoutTransform>
<TransformGroup>
<TransformGroup.Children>
<RotateTransform Angle="180" />
</TransformGroup.Children>
</TransformGroup>
</Grid.LayoutTransform>
<Ellipse Stroke="#FFA9A9A9" Name="circle" Width="19" Height="19" HorizontalAlignment="Center" VerticalAlignment="Center" />
<Ellipse Name="shadow" Width="17" Height="17" HorizontalAlignment="Center" VerticalAlignment="Center" Visibility="Hidden" />
<Path Data="M1,1.5L4.5,5 8,1.5" Stroke="#FF666666" StrokeThickness="2" Name="arrow" HorizontalAlignment="Center" VerticalAlignment="Center" SnapsToDevicePixels="False" />
</Grid>
<ContentPresenter RecognizesAccessKey="True" Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Margin="4,0,0,0" HorizontalAlignment="Left" VerticalAlignment="Center" SnapsToDevicePixels="True" Grid.Column="1" />
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsChecked">
<Setter Property="Path.Data" TargetName="arrow">
<Setter.Value>
<StreamGeometry>M1,4.5L4.5,1 8,4.5</StreamGeometry>
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
<Trigger Property="UIElement.IsMouseOver">
<Setter Property="Shape.Stroke" TargetName="circle">
<Setter.Value>
<SolidColorBrush>#FF666666</SolidColorBrush>
</Setter.Value>
</Setter>
<Setter Property="Shape.Stroke" TargetName="arrow">
<Setter.Value>
<SolidColorBrush>#FF222222</SolidColorBrush>
</Setter.Value>
</Setter>
<Setter Property="UIElement.Visibility" TargetName="shadow">
<Setter.Value>
<x:Static Member="Visibility.Visible" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
<Trigger.Value>
<x:Static Member="ExpandDirection.Up" />
</Trigger.Value>
</Trigger>
<Trigger Property="Expander.ExpandDirection">
<Setter Property="DockPanel.Dock" TargetName="ExpandSite">
<Setter.Value>
<x:Static Member="Dock.Left" />
</Setter.Value>
</Setter>
<Setter Property="DockPanel.Dock" TargetName="HeaderSite">
<Setter.Value>
<x:Static Member="Dock.Right" />
</Setter.Value>
</Setter>
<Setter Property="FrameworkElement.Style" TargetName="HeaderSite">
<Setter.Value>
<Style TargetType="ToggleButton">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate TargetType="ToggleButton">
<Border Padding="{TemplateBinding Control.Padding}">
<Grid Background="#00FFFFFF" SnapsToDevicePixels="False">
<Grid.RowDefinitions>
<RowDefinition Height="19" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Grid>
<Grid.LayoutTransform>
<TransformGroup>
<TransformGroup.Children>
<RotateTransform Angle="90" />
</TransformGroup.Children>
</TransformGroup>
</Grid.LayoutTransform>
<Ellipse Stroke="#FFA9A9A9" Name="circle" Width="19" Height="19" HorizontalAlignment="Center" VerticalAlignment="Center" />
<Ellipse Name="shadow" Width="17" Height="17" HorizontalAlignment="Center" VerticalAlignment="Center" Visibility="Hidden" />
<Path Data="M1,1.5L4.5,5 8,1.5" Stroke="#FF666666" StrokeThickness="2" Name="arrow" HorizontalAlignment="Center" VerticalAlignment="Center" SnapsToDevicePixels="False" />
</Grid>
<ContentPresenter RecognizesAccessKey="True" Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Margin="0,4,0,0" HorizontalAlignment="Center" VerticalAlignment="Top" SnapsToDevicePixels="True" Grid.Row="1" />
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsChecked">
<Setter Property="Path.Data" TargetName="arrow">
<Setter.Value>
<StreamGeometry>M1,4.5L4.5,1 8,4.5</StreamGeometry>
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
<Trigger Property="UIElement.IsMouseOver">
<Setter Property="Shape.Stroke" TargetName="circle">
<Setter.Value>
<SolidColorBrush>#FF666666</SolidColorBrush>
</Setter.Value>
</Setter>
<Setter Property="Shape.Stroke" TargetName="arrow">
<Setter.Value>
<SolidColorBrush>#FF222222</SolidColorBrush>
</Setter.Value>
</Setter>
<Setter Property="UIElement.Visibility" TargetName="shadow">
<Setter.Value>
<x:Static Member="Visibility.Visible" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>True</s:Boolean>
</Trigger.Value>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
<Trigger.Value>
<x:Static Member="ExpandDirection.Left" />
</Trigger.Value>
</Trigger>
<Trigger Property="UIElement.IsEnabled">
<Setter Property="TextElement.Foreground">
<Setter.Value>
<DynamicResource ResourceKey="{x:Static SystemColors.GrayTextBrushKey}" />
</Setter.Value>
</Setter>
<Trigger.Value>
<s:Boolean>False</s:Boolean>
</Trigger.Value>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>