Question

How do I style the Tab Control Border so that the selected Tab Item does not have a line underneath it?

These are my Tab Control and Tab Item styles so far.

<!-- Tab control styling -->
        <Style TargetType="{x:Type TabControl}">
            <Setter Property="Padding" Value="10,5,10,5" />
            <Setter Property="Margin" Value="3.5" />
            <Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.ControlLightBrushKey}}" />
        </Style>
        <!-- Tab item styling -->
        <Style TargetType="{x:Type TabItem}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TabItem}">
                        <Grid>
                            <Border 
                                 Name="Border"
                                 Background="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"
                                 BorderBrush="Black" 
                                 BorderThickness="1,1,1,0" 
                                 CornerRadius="3,3,0,0"
                                 MinWidth="120">
                                    <ContentPresenter x:Name="ContentSite"
                                        VerticalAlignment="Center"
                                        HorizontalAlignment="Center"
                                        ContentSource="Header"
                                        Margin="12,2,12,2"/>
                            </Border>
                        </Grid>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsFocused" Value="True" >
                                <Setter Property="Background" TargetName="Border" Value="{DynamicResource {x:Static SystemColors.ControlLightBrushKey}}" />
                                <Setter Property="HeaderTemplate">
                                    <Setter.Value>
                                        <DataTemplate>
                                            <TextBlock FontWeight="Bold" Text="{Binding}"/>
                                        </DataTemplate>
                                    </Setter.Value>
                                </Setter>
                            </Trigger>
                            <Trigger Property="IsMouseOver" Value="True" >
                                <Setter Property="Background" TargetName="Border" Value="{DynamicResource {x:Static SystemColors.ControlLightBrushKey}}" />
                                <Setter Property="HeaderTemplate">
                                    <Setter.Value>
                                        <DataTemplate>
                                            <TextBlock FontWeight="Bold" Text="{Binding}"/>
                                        </DataTemplate>
                                    </Setter.Value>
                                </Setter>
                            </Trigger>
                            <Trigger Property="IsSelected" Value="True" >
                                <Setter Property="Background" TargetName="Border" Value="{DynamicResource {x:Static SystemColors.ControlLightBrushKey}}" />
                                <Setter Property="HeaderTemplate">
                                    <Setter.Value>
                                        <DataTemplate>
                                            <TextBlock FontWeight="Bold" Text="{Binding}"/>
                                        </DataTemplate>
                                    </Setter.Value>
                                </Setter>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

If I can achieve the look displayed in the screenshot without having to overload the tab item control template then I don’t have an issue as the default tab item template doesn’t have the line underneath it on the selected tab. I haven’t been able to do this so far. Thanks for your help.

Answer 1

The XAML below is how I have overridden the TabControl to solve this problem. The key piece of info is the Margin property of the HeaderPanel. You will see that the bottom margin is -1, which shifts it down just enough to cover up that line.

    <Setter Property="Template">
        <Setter.Value>

            <ControlTemplate TargetType="{x:Type TabControl}">
                <Grid KeyboardNavigation.TabNavigation="Local">
                    <Grid.RowDefinitions>
                        <RowDefinition Height="Auto" />
                        <RowDefinition Height="*" />
                    </Grid.RowDefinitions>

                    <TabPanel x:Name="HeaderPanel"
                              Grid.Row="0"
                              Panel.ZIndex="1"
                              Margin="0,0,4,-1"
                              IsItemsHost="True"
                              KeyboardNavigation.TabIndex="1"
                              Background="Transparent" />

                    <Border x:Name="Border"
                            Grid.Row="1"
                            BorderThickness="1"
                            KeyboardNavigation.TabNavigation="Local"
                            KeyboardNavigation.DirectionalNavigation="Contained"
                            KeyboardNavigation.TabIndex="2">

                        <Border.Background>
                            <SolidColorBrush Color="White"/>
                        </Border.Background>

                        <Border.BorderBrush>
                            <SolidColorBrush Color="White"/>
                        </Border.BorderBrush>

                        <ContentPresenter x:Name="PART_SelectedContentHost"
                                          Margin="4"
                                          ContentSource="SelectedContent" />
                    </Border>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>