How to remove the dotted outline for the header of Expander control in WPF (C#)?

Question

How to remove the dotted outline for the header of Expander control in WPF (C#)?

I tried by making FocusVisualStyle to null but no luck. Is there any other approach?

<UserControl x:Class="MyControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Height="373" Width="669">
    <Expander FocusVisualStyle="{x:Null}" Expanded="expander1_Expanded" Focusable="False" Foreground="DarkBlue" Header="My Header" Height="219" Name="expander1" Width="525">

.....

Answer 1

You need to make the changes to this part (see the full template at the bottom of message) This example makes a thicker red stroke:

`<Style x:Key="ExpanderHeaderFocusVisual">
        <Setter Property="Control.Template">
            <Setter.Value>
                <ControlTemplate>
                    <Border>
                        <Rectangle Margin="0" SnapsToDevicePixels="true" Stroke="Red" StrokeThickness="2" StrokeDashArray="1 2"/>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>`

This is the original template for the expander as captured by Blend - it will automatically apply to all expanders in that window.

    `<Window.Resources>
        <Style x:Key="ExpanderRightHeaderStyle" TargetType="{x:Type ToggleButton}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ToggleButton}">
                        <Border Padding="{TemplateBinding Padding}">
                            <Grid Background="Transparent" SnapsToDevicePixels="False">
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="19"/>
                                    <RowDefinition Height="*"/>
                                </Grid.RowDefinitions>
                                <Grid>
                                    <Grid.LayoutTransform>
                                        <TransformGroup>
                                            <TransformGroup.Children>
                                                <TransformCollection>
                                                    <RotateTransform Angle="-90"/>
                                                </TransformCollection>
                                            </TransformGroup.Children>
                                        </TransformGroup>
                                    </Grid.LayoutTransform>
                                    <Ellipse x:Name="circle" HorizontalAlignment="Center" Height="19" Stroke="DarkGray" VerticalAlignment="Center" Width="19"/>
                                    <Path x:Name="arrow" Data="M 1,1.5 L 4.5,5 L 8,1.5" HorizontalAlignment="Center" SnapsToDevicePixels="false" Stroke="#666" StrokeThickness="2" VerticalAlignment="Center"/>
                                </Grid>
                                <ContentPresenter HorizontalAlignment="Center" Margin="0,4,0,0" Grid.Row="1" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Top"/>
                            </Grid>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsChecked" Value="true">
                                <Setter Property="Data" TargetName="arrow" Value="M 1,4.5  L 4.5,1  L 8,4.5"/>
                            </Trigger>
                            <Trigger Property="IsMouseOver" Value="true">
                                <Setter Property="Stroke" TargetName="circle" Value="#FF3C7FB1"/>
                                <Setter Property="Stroke" TargetName="arrow" Value="#222"/>
                            </Trigger>
                            <Trigger Property="IsPressed" Value="true">
                                <Setter Property="Stroke" TargetName="circle" Value="#FF526C7B"/>
                                <Setter Property="StrokeThickness" TargetName="circle" Value="1.5"/>
                                <Setter Property="Stroke" TargetName="arrow" Value="#FF003366"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="ExpanderUpHeaderStyle" TargetType="{x:Type ToggleButton}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ToggleButton}">
                        <Border Padding="{TemplateBinding Padding}">
                            <Grid Background="Transparent" SnapsToDevicePixels="False">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="19"/>
                                    <ColumnDefinition Width="*"/>
                                </Grid.ColumnDefinitions>
                                <Grid>
                                    <Grid.LayoutTransform>
                                        <TransformGroup>
                                            <TransformGroup.Children>
                                                <TransformCollection>
                                                    <RotateTransform Angle="180"/>
                                                </TransformCollection>
                                            </TransformGroup.Children>
                                        </TransformGroup>
                                    </Grid.LayoutTransform>
                                    <Ellipse x:Name="circle" HorizontalAlignment="Center" Height="19" Stroke="DarkGray" VerticalAlignment="Center" Width="19"/>
                                    <Path x:Name="arrow" Data="M 1,1.5 L 4.5,5 L 8,1.5" HorizontalAlignment="Center" SnapsToDevicePixels="false" Stroke="#666" StrokeThickness="2" VerticalAlignment="Center"/>
                                </Grid>
                                <ContentPresenter Grid.Column="1" HorizontalAlignment="Left" Margin="4,0,0,0" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Center"/>
                            </Grid>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsChecked" Value="true">
                                <Setter Property="Data" TargetName="arrow" Value="M 1,4.5  L 4.5,1  L 8,4.5"/>
                            </Trigger>
                            <Trigger Property="IsMouseOver" Value="true">
                                <Setter Property="Stroke" TargetName="circle" Value="#FF3C7FB1"/>
                                <Setter Property="Stroke" TargetName="arrow" Value="#222"/>
                            </Trigger>
                            <Trigger Property="IsPressed" Value="true">
                                <Setter Property="Stroke" TargetName="circle" Value="#FF526C7B"/>
                                <Setter Property="StrokeThickness" TargetName="circle" Value="1.5"/>
                                <Setter Property="Stroke" TargetName="arrow" Value="#FF003366"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="ExpanderLeftHeaderStyle" TargetType="{x:Type ToggleButton}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ToggleButton}">
                        <Border Padding="{TemplateBinding Padding}">
                            <Grid Background="Transparent" SnapsToDevicePixels="False">
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="19"/>
                                    <RowDefinition Height="*"/>
                                </Grid.RowDefinitions>
                                <Grid>
                                    <Grid.LayoutTransform>
                                        <TransformGroup>
                                            <TransformGroup.Children>
                                                <TransformCollection>
                                                    <RotateTransform Angle="90"/>
                                                </TransformCollection>
                                            </TransformGroup.Children>
                                        </TransformGroup>
                                    </Grid.LayoutTransform>
                                    <Ellipse x:Name="circle" HorizontalAlignment="Center" Height="19" Stroke="DarkGray" VerticalAlignment="Center" Width="19"/>
                                    <Path x:Name="arrow" Data="M 1,1.5 L 4.5,5 L 8,1.5" HorizontalAlignment="Center" SnapsToDevicePixels="false" Stroke="#666" StrokeThickness="2" VerticalAlignment="Center"/>
                                </Grid>
                                <ContentPresenter HorizontalAlignment="Center" Margin="0,4,0,0" Grid.Row="1" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Top"/>
                            </Grid>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsChecked" Value="true">
                                <Setter Property="Data" TargetName="arrow" Value="M 1,4.5  L 4.5,1  L 8,4.5"/>
                            </Trigger>
                            <Trigger Property="IsMouseOver" Value="true">
                                <Setter Property="Stroke" TargetName="circle" Value="#FF3C7FB1"/>
                                <Setter Property="Stroke" TargetName="arrow" Value="#222"/>
                            </Trigger>
                            <Trigger Property="IsPressed" Value="true">
                                <Setter Property="Stroke" TargetName="circle" Value="#FF526C7B"/>
                                <Setter Property="StrokeThickness" TargetName="circle" Value="1.5"/>
                                <Setter Property="Stroke" TargetName="arrow" Value="#FF003366"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="ExpanderHeaderFocusVisual">
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <Border>
                            <Rectangle Margin="0" SnapsToDevicePixels="true" Stroke="Black" StrokeThickness="1" StrokeDashArray="1 2"/>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="ExpanderDownHeaderStyle" TargetType="{x:Type ToggleButton}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ToggleButton}">
                        <Border Padding="{TemplateBinding Padding}">
                            <Grid Background="Transparent" SnapsToDevicePixels="False">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="19"/>
                                    <ColumnDefinition Width="*"/>
                                </Grid.ColumnDefinitions>
                                <Ellipse x:Name="circle" HorizontalAlignment="Center" Height="19" Stroke="DarkGray" VerticalAlignment="Center" Width="19"/>
                                <Path x:Name="arrow" Data="M 1,1.5 L 4.5,5 L 8,1.5" HorizontalAlignment="Center" SnapsToDevicePixels="false" Stroke="#666" StrokeThickness="2" VerticalAlignment="Center"/>
                                <ContentPresenter Grid.Column="1" HorizontalAlignment="Left" Margin="4,0,0,0" RecognizesAccessKey="True" SnapsToDevicePixels="True" VerticalAlignment="Center"/>
                            </Grid>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsChecked" Value="true">
                                <Setter Property="Data" TargetName="arrow" Value="M 1,4.5  L 4.5,1  L 8,4.5"/>
                            </Trigger>
                            <Trigger Property="IsMouseOver" Value="true">
                                <Setter Property="Stroke" TargetName="circle" Value="#FF3C7FB1"/>
                                <Setter Property="Stroke" TargetName="arrow" Value="#222"/>
                            </Trigger>
                            <Trigger Property="IsPressed" Value="true">
                                <Setter Property="Stroke" TargetName="circle" Value="#FF526C7B"/>
                                <Setter Property="StrokeThickness" TargetName="circle" Value="1.5"/>
                                <Setter Property="Stroke" TargetName="arrow" Value="#FF003366"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="StyledExpander" TargetType="{x:Type Expander}">
            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
            <Setter Property="Background" Value="Transparent"/>
            <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
            <Setter Property="VerticalContentAlignment" Value="Stretch"/>
            <Setter Property="BorderBrush" Value="Transparent"/>
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type Expander}">
                        <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="3" SnapsToDevicePixels="true">
                            <DockPanel>
                                <ToggleButton x:Name="HeaderSite" ContentTemplate="{TemplateBinding HeaderTemplate}" ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}" Content="{TemplateBinding Header}" DockPanel.Dock="Top" Foreground="{TemplateBinding Foreground}" FontWeight="{TemplateBinding FontWeight}" FocusVisualStyle="{StaticResource ExpanderHeaderFocusVisual}" FontStyle="{TemplateBinding FontStyle}" FontStretch="{TemplateBinding FontStretch}" FontSize="{TemplateBinding FontSize}" FontFamily="{TemplateBinding FontFamily}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" IsChecked="{Binding IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Margin="1" MinWidth="0" MinHeight="0" Padding="{TemplateBinding Padding}" Style="{StaticResource ExpanderDownHeaderStyle}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                                <ContentPresenter x:Name="ExpandSite" DockPanel.Dock="Bottom" Focusable="false" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" Visibility="Collapsed" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
                            </DockPanel>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsExpanded" Value="true">
                                <Setter Property="Visibility" TargetName="ExpandSite" Value="Visible"/>
                            </Trigger>
                            <Trigger Property="ExpandDirection" Value="Right">
                                <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Right"/>
                                <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Left"/>
                                <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderRightHeaderStyle}"/>
                            </Trigger>
                            <Trigger Property="ExpandDirection" Value="Up">
                                <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Top"/>
                                <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Bottom"/>
                                <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderUpHeaderStyle}"/>
                            </Trigger>
                            <Trigger Property="ExpandDirection" Value="Left">
                                <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Left"/>
                                <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Right"/>
                                <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderLeftHeaderStyle}"/>
                            </Trigger>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="ExpanderWithDifferentFocusRectagle" TargetType="{x:Type Expander}">
            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
            <Setter Property="Background" Value="Transparent"/>
            <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
            <Setter Property="VerticalContentAlignment" Value="Stretch"/>
            <Setter Property="BorderBrush" Value="Transparent"/>
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type Expander}">
                        <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="3" SnapsToDevicePixels="true">
                            <DockPanel>
                                <ToggleButton x:Name="HeaderSite" ContentTemplate="{TemplateBinding HeaderTemplate}" ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}" Content="{TemplateBinding Header}" DockPanel.Dock="Top" Foreground="{TemplateBinding Foreground}" FontWeight="{TemplateBinding FontWeight}" FocusVisualStyle="{StaticResource ExpanderHeaderFocusVisual}" FontStyle="{TemplateBinding FontStyle}" FontStretch="{TemplateBinding FontStretch}" FontSize="{TemplateBinding FontSize}" FontFamily="{TemplateBinding FontFamily}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" IsChecked="{Binding IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Margin="1" MinWidth="0" MinHeight="0" Padding="{TemplateBinding Padding}" Style="{StaticResource ExpanderDownHeaderStyle}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"/>
                                <ContentPresenter x:Name="ExpandSite" DockPanel.Dock="Bottom" Focusable="false" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" Visibility="Collapsed" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
                            </DockPanel>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsExpanded" Value="true">
                                <Setter Property="Visibility" TargetName="ExpandSite" Value="Visible"/>
                            </Trigger>
                            <Trigger Property="ExpandDirection" Value="Right">
                                <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Right"/>
                                <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Left"/>
                              <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderRightHeaderStyle}"/>
                            </Trigger>
                            <Trigger Property="ExpandDirection" Value="Up">
                                <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Top"/>
                                <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Bottom"/>
                                <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderUpHeaderStyle}"/>
                            </Trigger>
                            <Trigger Property="ExpandDirection" Value="Left">
                                <Setter Property="DockPanel.Dock" TargetName="ExpandSite" Value="Left"/>
                                <Setter Property="DockPanel.Dock" TargetName="HeaderSite" Value="Right"/>
                                <Setter Property="Style" TargetName="HeaderSite" Value="{StaticResource ExpanderLeftHeaderStyle}"/>
                            </Trigger>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>`