<Expander Width="240" x:Name="myExpander">
<Expander.Header>
<StackPanel Orientation="Horizontal" >
<TextBlock Text="内容" />
<Image Width="20" Margin="15,0,0,0">
<Image.Style>
<Style TargetType="Image">
<Style.Triggers>
<DataTrigger Binding="{Binding IsExpanded, ElementName=myExpander}" Value="True">
<Setter Property="Source" Value="图片路径1"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsExpanded, ElementName=myExpander}" Value="False">
<Setter Property="Source" Value="图片路径2"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Image.Style>
</Image>
</StackPanel>
</Expander.Header>
<Expander.Template>
<ControlTemplate TargetType="Expander">
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}">
<DockPanel>
<ToggleButton x:Name="HeaderSite" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" IsChecked="{Binding IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Content="{TemplateBinding Header}" ContentTemplate="{TemplateBinding HeaderTemplate}" ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}" DockPanel.Dock="Top"/>
<ContentPresenter x:Name="ExpandSite" DockPanel.Dock="Bottom" Focusable="false" Visibility="Collapsed" Margin="{TemplateBinding Padding}">
<ContentPresenter.LayoutTransform>
<TransformGroup>
<TranslateTransform x:Name="ExpandTranform"/>
</TransformGroup>
</ContentPresenter.LayoutTransform>
</ContentPresenter>
</DockPanel>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsExpanded" Value="True">
<Setter Property="Visibility" TargetName="ExpandSite" Value="Visible"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Expander.Template>
<StackPanel>
<RadioButton Content="RadioButton按钮" />
</StackPanel>
</Expander>