目标名称的WPF样式触发器无法正常工作

Question

I have an issue setting the Foreground color in a ControlTemplate with triggers.

            <LinearGradientBrush x:Key="TabItemDefaultBackgroundBrush" StartPoint="0,0" EndPoint="0,1">
                <GradientBrush.GradientStops>
                    <GradientStopCollection>
                        <GradientStop Offset="0.0" Color="#FFF" />
                        <GradientStop Offset="1.0" Color="#EEE" />
                    </GradientStopCollection>
                </GradientBrush.GradientStops>
            </LinearGradientBrush>

            <SolidColorBrush x:Key="SolidBorderBrush" Color="#888" />
            <SolidColorBrush x:Key="TabItemSelectBackgroundBrush" Color="#69C" />
            <SolidColorBrush x:Key="PressedBrush" Color="#79C" />
            <Style TargetType="{x:Type TabItem}">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="{x:Type TabItem}">
                            <Grid>
                                <Border
                                    Name="tabBorder"
                                    MinWidth="150"
                                    MinHeight="50"
                                    Margin="0,0,20,0"
                                    Background="{StaticResource TabItemDefaultBackgroundBrush}"
                                    BorderBrush="{StaticResource SolidBorderBrush}"
                                    BorderThickness="1"
                                    CornerRadius="1,1,1,1">
                                    <Grid>
                                        <Grid >
                                            <TextBlock Name="HeaderHeader">
                                                </TextBlock>
                                        </Grid>
                                        <ContentPresenter
                                            x:Name="ContentSite"
                                            Margin="12,2,12,2"
                                            HorizontalAlignment="Center"
                                            VerticalAlignment="Center"
                                            ContentSource="Header"
                                            RecognizesAccessKey="True" />
                                    </Grid>
                                </Border>
                            </Grid>
                            <ControlTemplate.Triggers>
                                <Trigger Property="IsSelected" Value="True">
                                    <Setter TargetName="HeaderHeader" Property="Foreground" Value="White" />
                                    <Setter TargetName="tabBorder" Property="Background" Value="{StaticResource TabItemSelectBackgroundBrush}" />
                                </Trigger>
                            </ControlTemplate.Triggers>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>

When the tab is selected, the background border 'tabBorder' is set correctly, but the foreground of textblock 'HeaderHeader' does not respond.

<ControlTemplate.Triggers>
    <Trigger Property="IsSelected" Value="True">
        <Setter TargetName="HeaderHeader" Property="Foreground" Value="White" />
        <Setter TargetName="tabBorder" Property="Background" Value="{StaticResource TabItemSelectBackgroundBrush}" />
    </Trigger>
</ControlTemplate.Triggers>

When I remove the TargetName and set the foreground white (to all components), it does work. (but obviously also the foreground color of everything in the content pre

<ControlTemplate.Triggers>
    <Trigger Property="IsSelected" Value="True">
        <Setter Property="Foreground" Value="White" />
        <Setter TargetName="tabBorder" Property="Background" Value="{StaticResource TabItemSelectBackgroundBrush}" />
    </Trigger>
</ControlTemplate.Triggers>

Even stranger, when I put the TargetName back in place, but change the setter property from foreground to background, it DOES work! Then the background is set to white for the selected tab.

<ControlTemplate.Triggers>
    <Trigger Property="IsSelected" Value="True">
        <Setter TargetName="HeaderHeader" Property="Background" Value="White" />
        <Setter TargetName="tabBorder" Property="Background" Value="{StaticResource TabItemSelectBackgroundBrush}" />
    </Trigger>
</ControlTemplate.Triggers>

Why on earth is it not working for what I need (=set foreground for selected tab)?!

Answer 1

Aha, I learned something today... I was looking in the wrong direction ! After googling more on "ControlTemplate" something finally sunk in. The ContentPresenter does not show the information of the tab, it shows the label of the tab and nothing more. So my trigger was working just fine, but it was setting the foreground of a textblock which had no meaning at all!

When I change the trigger to which control actually shows the label, it was easy peasy...

<Setter TargetName="ContentSite" Property="TextElement.Foreground" Value="White" />

I did have to use an attached property 'TextElement' in order to be able to set properties on text elements.