c# - HighlightBrushKey を動的に設定するには?

Question

ここに私のコードがあります -

<Style x:Key="CustomComboBox" TargetType="{x:Type ComboBox}">
    <Setter Property="SnapsToDevicePixels" Value="true"/>
    <Setter Property="FontSize" Value="18"/>
    <Setter Property="Background" Value="LightGray"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ComboBox}">
                <Grid>
                    <Grid.Resources>
// This part, I want to set dynamically
                        <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="{TemplateBinding BorderBrush}"></SolidColorBrush>
                    </Grid.Resources>
                    <ToggleButton Grid.Column="2" Template="{StaticResource ComboBoxToggleButton}" x:Name="ToggleButton" Focusable="false" IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Press" Background="{TemplateBinding Background}" Foreground="{TemplateBinding Foreground}" BorderBrush="{TemplateBinding BorderBrush}"/>
                    <ContentPresenter HorizontalAlignment="Left" Margin="10,3,23,3" x:Name="Content" VerticalAlignment="Center" Content="{TemplateBinding SelectionBoxItem}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" IsHitTestVisible="False"/>
                    <TextBox x:Name="PART_EditableTextBox" Visibility="Hidden" Template="{StaticResource ComboBoxTextBox}" HorizontalAlignment="Left" Margin="3,3,23,3" Style="{x:Null}" VerticalAlignment="Center" Focusable="True" Background="{TemplateBinding Background}" Foreground="{TemplateBinding Foreground}" IsReadOnly="{TemplateBinding IsReadOnly}" FontSize="{TemplateBinding FontSize}"/>
                                            <Popup Placement="Center" x:Name="Popup" Focusable="False" AllowsTransparency="True" 
                           IsOpen="{TemplateBinding IsDropDownOpen}"  PopupAnimation="Fade" VerticalOffset="-2">

                        <Grid MinWidth="{TemplateBinding ActualWidth}" MaxHeight="{TemplateBinding MaxDropDownHeight}"
                              x:Name="DropDown" SnapsToDevicePixels="True">
                            <Border BorderBrush="LightGray" BorderThickness="1,1,1,1" x:Name="DropDownBorder" Background="White"  />
                            <ScrollViewer x:Name="ScrollViewer" Template="{DynamicResource CustomScrollViewerControlTemplate}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="0" Margin="4,6,4,6" SnapsToDevicePixels="True" HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto" CanContentScroll="True">
                               <ItemsPresenter KeyboardNavigation.DirectionalNavigation="Contained" />
                            </ScrollViewer>
                        </Grid>
                    </Popup>
                </Grid>
                <ControlTemplate.Triggers>
                        <Trigger Property="HasItems" Value="false">
                        <Setter Property="MinHeight" Value="95" TargetName="DropDownBorder"/>
                    </Trigger>
                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Foreground" Value="LightGray"/>
                    </Trigger>
                    <Trigger Property="IsGrouping" Value="true">
                        <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
                    </Trigger>
                    <Trigger Property="AllowsTransparency" SourceName="Popup" Value="true">
                        <Setter Property="Margin" Value="0,2,0,0" TargetName="DropDownBorder"/>
                    </Trigger>
                    <Trigger Property="IsEditable" Value="true">
                        <Setter Property="IsTabStop" Value="false"/>
                        <Setter Property="Visibility" Value="Visible" TargetName="PART_EditableTextBox"/>
                        <Setter Property="Visibility" Value="Hidden" TargetName="ContentSite"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

カスタムコンボボックスを作成しています。ここでは、ComboBox の TemplateBinding から BorderBrush 値を取得しようとしています。しかし、私はそれを取得していません。いつも白です。ブラシを取得する方法が間違っている可能性があります。

提案してください。