WPF Change value of Element's Property from BasedOn - wpf

Question

I have the following style:
<Style TargetType="{x:Type local:MetroTabControl}">
<Style.Triggers>
<Trigger Property="SingleRow" Value="True">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:MetroTabControl}">
<Grid>
<Grid KeyboardNavigation.TabNavigation="Local" SnapsToDevicePixels="True">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Grid>
<ScrollViewer x:Name="ScrollViewer" VerticalScrollBarVisibility="Disabled" HorizontalScrollBarVisibility="Hidden" Style="{DynamicResource TabPanelScrollViewer}">
<TabPanel x:Name="HeaderPanel" IsItemsHost="True" Panel.ZIndex="1" KeyboardNavigation.TabIndex="1"/>
</ScrollViewer>
<Button x:Name="AddTabItem" Content="" Style="{DynamicResource TabControlButton}" HorizontalAlignment="Right" VerticalAlignment="Top"/>
</Grid>
<Border Grid.Row="1" x:Name="TabPanelBorder" Background="Transparent">
<Rectangle x:Name="TabPanelBorderRectangle" Fill="{StaticResource TabPanelBorderBrush}" Height="2"/>
</Border>
<Border Grid.Row="2" Background="{StaticResource TabControlBackground}"/>
<ContentPresenter Grid.Row="2" Name="PART_SelectedContentHost" ContentSource="SelectedContent"/>
</Grid>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
<!--<Setter Property="Template" Value="{StaticResource MetroTabControlSingleRow}" />-->
</Trigger>
<Trigger Property="SingleRow" Value="False">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type local:MetroTabControl}">
<Grid KeyboardNavigation.TabNavigation="Local" SnapsToDevicePixels="True">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<Border Background="Transparent" BorderThickness="0,0,0,2" BorderBrush="{StaticResource TabPanelBorderBrush}">
<DockPanel LastChildFill="True">
<Button x:Name="AddTabItem" Style="{DynamicResource TabControlButton}" DockPanel.Dock="Right">
<Path Stroke="{Binding Foreground, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type Button}}}" Data="M0,4 H8 M4,0 V8" StrokeThickness="2" />
</Button>
<TabPanel x:Name="HeaderPanel" IsItemsHost="True" Panel.ZIndex="1" KeyboardNavigation.TabIndex="1"/>
</DockPanel>
</Border>
<Border Grid.Row="1" Background="{StaticResource TabControlBackground}"/>
<ContentPresenter Grid.Row="1" Name="PART_SelectedContentHost" ContentSource="SelectedContent"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
<!--<Setter Property="Template" Value="{StaticResource MetroTabControlMultiRows}" />-->
</Trigger>
</Style.Triggers>
</Style>
I want to have another style, BasedOn the above, but with one change - I want to change the Fill Color of the TabPanelBorderRectangle Rectangle.
So, to use the BasedOn I wrote the following:
<Style TargetType="{x:Type local:MetroTabControl}" BasedOn="{StaticResource {x:Type local:MetroTabControl}}">
</Style>
But I have no Idea how to change the color of the TabPanelBorderRectangle Rectangle from the BasedOn Style.
I tried something like
<Setter TargetName="TabPanelBorderRectangle" Property="Fill" Value="Red"/>
but it doesnt work (TargetName property cannot be set on a Style Setter)
..
How can I do this?

Answer 1

As error states you cannot use TargetName in style setters.
As a workaround what you can do is, instead of using StaticResource for your brush, bind it using DynamicResource so that we can take advantage of resource look up behaviour of XAML.
<Rectangle x:Name="TabPanelBorderRectangle"
Fill="{DynamicResource TabPanelBorderBrush}"/>
Now, in your style you can override that brush by specifying the same key for a brush and provide your color value there.
<Style TargetType="{x:Type local:MetroTabControl}"
BasedOn="{StaticResource {x:Type local:MetroTabControl}}">
<Style.Resources>
<SolidColorBrush x:Key="TabPanelBorderBrush" Color="Green"/>
</Style.Resources>
</Style>
Since the brush is binded via dynamic resource it will pick the most local value from your style resource which will be Green in above case.