How Do I Change The Text Foreground of a WPF TabItem With Nested Text?

Question

I'm looking to have the foreground of the text of a TabItem change whenever the tab becomes active. I was using the following, which was working fine until I changed the type of content being displayed in the tab:

<TabControl Style="{DynamicResource SidebarTabControl}">
    <TabItem Header="TabItem" Style="{DynamicResource SidebarTab}" />
</TabControl>

<Style x:Key="SidebarTabForegroundStyleSelected">
    <Setter Property="TextBlock.Foreground" Value="White" />
</Style>

<Style x:Key="SidebarTabForegroundStyle">
    <Setter Property="TextBlock.Foreground" Value="Black" />
</Style>

<Style x:Key="SidebarTab" TargetType="TabItem">
    <Setter Property="Padding" Value="10,12,2,12" />
    <Setter Property="BorderThickness" Value="0,1,0,1" />
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type TabItem}">
                <Border Padding="{TemplateBinding Padding}" 
                    Name="tab" 
                    BorderThickness="{TemplateBinding BorderThickness}" 
                    BorderBrush="{StaticResource SidebarTabBorderBrush}"
                    SnapsToDevicePixels="True">
                    <ContentPresenter Style="{StaticResource SidebarTabForegroundStyle}" Name="content" ContentSource="Header" />
                </Border>

                <ControlTemplate.Triggers>
                    <Trigger Property="IsSelected" Value="True">
                        <Setter TargetName="tab" Property="Background" Value="{StaticResource SidebarTabBackgroundBrushSelected}" />
                        <Setter TargetName="tab" Property="BorderBrush" Value="{StaticResource SidebarTabBorderBrushSelected}" />
                        <Setter TargetName="content" Property="Style" Value="{StaticResource SidebarTabForegroundStyleSelected}" />
                    </Trigger>
                    <Trigger Property="IsSelected" Value="False">
                        <Setter TargetName="tab" Property="Background" Value="{StaticResource SidebarTabBackgroundBrush}" />
                        <Setter TargetName="tab" Property="BorderBrush" Value="{StaticResource SidebarTabBorderBrush}" />
                        <Setter TargetName="content" Property="Style" Value="{StaticResource SidebarTabForegroundStyle}" />
                    </Trigger>
                </ControlTemplate.Triggers>

            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

When I changed the TabItem to:

<TabControl Style="{DynamicResource SidebarTabControl}">
    <TabItem Style="{DynamicResource SidebarTab}">
        <TabItem.Header>
            <StackPanel Orientation="Horizontal">
                <Image Height="16" Source="..\..\Icons\cog.png" />
                <TextBlock Text="TabItem" Margin="5,0,0,0" VerticalAlignment="Center" />
            </StackPanel>
        </TabItem.Header>
    </TabItem>
</TabControl>

The foreground of the text no longer turns to white when the tab is selected and back to black when the tab is no longer selected. Everything else still works correctly.

Does anyone know if there is a way to accomplish changing the color of the foreground in the XAML above?

Answer 1

It looks like the issue is coming up because you are setting the wrong property:

<Style x:Key="SidebarTabForegroundStyleSelected">
    <Setter Property="TextBox.Foreground" Value="White" />
</Style>

<Style x:Key="SidebarTabForegroundStyle">
    <Setter Property="TextBox.Foreground" Value="Black" />
</Style>

You need to be setting TextElement.Foreground or TextBlock.Foreground

Also, since it is an inherited property, you can just set the AttachedProperty directly on the TabItems, you don't need to assign it specifically to the content.

<TabControl Style="{DynamicResource SidebarTabControl}">
 <TabControl.ItemContainerStyle>
  <Style TargetType="{x:Type TabItem}">
   <Style.Triggers>
    <Trigger Property="IsSelected"
       Value="True">
     <Setter Property="TextElement.Foreground"
       Value="Red" />
    </Trigger>
   </Style.Triggers>
  </Style>
 </TabControl.ItemContainerStyle>
 <TabItem>
  <TabItem.Header>
   <StackPanel Orientation="Horizontal">
    <Image Height="16"
        Source="..\..\Icons\cog.png" />
    <TextBlock Text="TabItem"
         Margin="5,0,0,0"
         VerticalAlignment="Center" />
   </StackPanel>
  </TabItem.Header>
  Item 1
 </TabItem>
 <TabItem>
  <TabItem.Header>
   <TextBlock Text="Tab 2" />
  </TabItem.Header>
  Item 2
 </TabItem>
 <TabItem Header="Item 3">
     Item 3
 </TabItem>
</TabControl>

Answer 2

Move the trigger from the control template to the style:

<Grid>
    <Grid.Resources>
        <SolidColorBrush x:Key="SidebarTabBackgroundBrushSelected" Color="Gray"></SolidColorBrush>
        <SolidColorBrush x:Key="SidebarTabBorderBrushSelected" Color="Blue"></SolidColorBrush>
        <SolidColorBrush x:Key="SidebarTabBackgroundBrush" Color="LightGray"></SolidColorBrush>
        <SolidColorBrush x:Key="SidebarTabBorderBrush" Color="Green"></SolidColorBrush>

        <Style x:Key="SidebarTab" TargetType="TabItem">
            <Setter Property="Padding" Value="10,12,2,12" />
            <Setter Property="BorderThickness" Value="0,1,0,1" />
            <Setter Property="Foreground"  Value="Blue"></Setter>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TabItem}">
                        <Border Padding="{TemplateBinding Padding}" 
                Name="tab" 
                BorderThickness="{TemplateBinding BorderThickness}" 
                BorderBrush="{StaticResource SidebarTabBorderBrush}"
                SnapsToDevicePixels="True">
                            <ContentPresenter Name="content"
                                              ContentSource="Header" />
                        </Border>

                        <ControlTemplate.Triggers>
                            <Trigger Property="IsSelected" Value="True">
                                <Setter TargetName="tab" Property="Background" Value="{StaticResource SidebarTabBackgroundBrushSelected}" />
                                <Setter TargetName="tab" Property="BorderBrush" Value="{StaticResource SidebarTabBorderBrushSelected}" />
                            </Trigger>
                            <Trigger Property="IsSelected" Value="False">
                                <Setter TargetName="tab" Property="Background" Value="{StaticResource SidebarTabBackgroundBrush}" />
                                <Setter TargetName="tab" Property="BorderBrush" Value="{StaticResource SidebarTabBorderBrush}" />
                            </Trigger>
                        </ControlTemplate.Triggers>

                    </ControlTemplate>
                </Setter.Value>
            </Setter>
            <Style.Triggers>
                <Trigger Property="IsSelected" Value="True">
                    <Setter Property="Foreground" Value="Red"></Setter>
                </Trigger>
                </Style.Triggers>
        </Style>
    </Grid.Resources>
    <TabControl Style="{DynamicResource SidebarTabControl}">
        <TabItem Header="TabItem 1" Style="{DynamicResource SidebarTab}" />
        <TabItem Style="{DynamicResource SidebarTab}"  >
            <TabItem.Header>
                <StackPanel>
                    <TextBlock Text="a"></TextBlock>
                    <TextBlock Text="b"></TextBlock>
                </StackPanel>
            </TabItem.Header>
        </TabItem>
        <TabItem Header="TabItem 3" Style="{DynamicResource SidebarTab}" />
    </TabControl>
</Grid>