C# WPF making tabitem border slightly thicker

Question

I would like to have a thicker border for my tabitems, without changing the default behavior.

I've done some research and it seems that I need to work with ControlTemplate, but this overrides the default behaviour (i.e. the background color is gone, the background color stays the same regardless it is selected or not. tab header is not highlighted in blue when I hover the mouse cursor on the tab header, etc..)

How can I just adjust the border, without messing up the current behavior?

Thanks!

Answer 1

First thing to say is that tabItem is not responsible for how the tabcontrol content looks.

You have 2 options. First one is to download Blend. Make a copy of default styles for TabItem and TabControl and make your changes there. It's much easier than it sounds

Second one is to do the following:

        private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        var tabControlContentPanel = tb.Template.FindName("ContentPanel", tb) as Border;
        tabControlContentPanel.BorderThickness = new Thickness(10);

        foreach (TabItem tabItem in tb.Items)
        {
            var tabItemHeader = tabItem.Template.FindName("Bd", tabItem) as Border;
            tabItemHeader.BorderThickness = new Thickness(10);
        }
    }

Just be sure that TabControl and TabItems are loaded, otherwise "FindName" would return null

Update:

I'll share with you default styles for TabControl and TabItem, but I strongly recommend you to take a look at Blend. Use them like this:

 <TabControl HorizontalAlignment="Left" MouseDown="tb_MouseDown" Name="tb" Height="300" VerticalAlignment="Top" Style="{DynamicResource TabControlStyle1}">
            <TabItem Header="TabItem" Style="{DynamicResource TabItemStyle1}" >
                <Grid Background="#FFE5E5E5"/>
            </TabItem>
</TabControl>

Styles:

 <Window.Resources>
        <SolidColorBrush x:Key="TabControlNormalBorderBrush" Color="#8C8E94"/>
        <Style x:Key="TabControlStyle1" TargetType="{x:Type TabControl}">
            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
            <Setter Property="Padding" Value="4,4,4,4"/>
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="BorderBrush" Value="{StaticResource TabControlNormalBorderBrush}"/>
            <Setter Property="Background" Value="#F9F9F9"/>
            <Setter Property="HorizontalContentAlignment" Value="Center"/>
            <Setter Property="VerticalContentAlignment" Value="Center"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TabControl}">
                        <Grid ClipToBounds="true" SnapsToDevicePixels="true" KeyboardNavigation.TabNavigation="Local">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition x:Name="ColumnDefinition0"/>
                                <ColumnDefinition x:Name="ColumnDefinition1" Width="0"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition x:Name="RowDefinition0" Height="Auto"/>
                                <RowDefinition x:Name="RowDefinition1" Height="*"/>
                            </Grid.RowDefinitions>
                            <TabPanel x:Name="HeaderPanel" Grid.Column="0" IsItemsHost="true" Margin="2,2,2,0" Grid.Row="0" KeyboardNavigation.TabIndex="1" Panel.ZIndex="1"/>
                            <Border x:Name="ContentPanel" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="0" KeyboardNavigation.DirectionalNavigation="Contained" Grid.Row="1" KeyboardNavigation.TabIndex="2" KeyboardNavigation.TabNavigation="Local">
                                <ContentPresenter x:Name="PART_SelectedContentHost" ContentSource="SelectedContent" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            </Border>
                        </Grid>
                        <ControlTemplate.Triggers>
                            <Trigger Property="TabStripPlacement" Value="Bottom">
                                <Setter Property="Grid.Row" TargetName="HeaderPanel" Value="1"/>
                                <Setter Property="Grid.Row" TargetName="ContentPanel" Value="0"/>
                                <Setter Property="Height" TargetName="RowDefinition0" Value="*"/>
                                <Setter Property="Height" TargetName="RowDefinition1" Value="Auto"/>
                                <Setter Property="Margin" TargetName="HeaderPanel" Value="2,0,2,2"/>
                            </Trigger>
                            <Trigger Property="TabStripPlacement" Value="Left">
                                <Setter Property="Grid.Row" TargetName="HeaderPanel" Value="0"/>
                                <Setter Property="Grid.Row" TargetName="ContentPanel" Value="0"/>
                                <Setter Property="Grid.Column" TargetName="HeaderPanel" Value="0"/>
                                <Setter Property="Grid.Column" TargetName="ContentPanel" Value="1"/>
                                <Setter Property="Width" TargetName="ColumnDefinition0" Value="Auto"/>
                                <Setter Property="Width" TargetName="ColumnDefinition1" Value="*"/>
                                <Setter Property="Height" TargetName="RowDefinition0" Value="*"/>
                                <Setter Property="Height" TargetName="RowDefinition1" Value="0"/>
                                <Setter Property="Margin" TargetName="HeaderPanel" Value="2,2,0,2"/>
                            </Trigger>
                            <Trigger Property="TabStripPlacement" Value="Right">
                                <Setter Property="Grid.Row" TargetName="HeaderPanel" Value="0"/>
                                <Setter Property="Grid.Row" TargetName="ContentPanel" Value="0"/>
                                <Setter Property="Grid.Column" TargetName="HeaderPanel" Value="1"/>
                                <Setter Property="Grid.Column" TargetName="ContentPanel" Value="0"/>
                                <Setter Property="Width" TargetName="ColumnDefinition0" Value="*"/>
                                <Setter Property="Width" TargetName="ColumnDefinition1" Value="Auto"/>
                                <Setter Property="Height" TargetName="RowDefinition0" Value="*"/>
                                <Setter Property="Height" TargetName="RowDefinition1" Value="0"/>
                                <Setter Property="Margin" TargetName="HeaderPanel" Value="0,2,2,2"/>
                            </Trigger>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style x:Key="TabItemFocusVisual">
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <Rectangle Margin="3,3,3,1" SnapsToDevicePixels="true" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <LinearGradientBrush x:Key="ButtonNormalBackground" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="#F3F3F3" Offset="0"/>
            <GradientStop Color="#EBEBEB" Offset="0.5"/>
            <GradientStop Color="#DDDDDD" Offset="0.5"/>
            <GradientStop Color="#CDCDCD" Offset="1"/>
        </LinearGradientBrush>
        <LinearGradientBrush x:Key="TabItemHotBackground" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="#EAF6FD" Offset="0.15"/>
            <GradientStop Color="#D9F0FC" Offset=".5"/>
            <GradientStop Color="#BEE6FD" Offset=".5"/>
            <GradientStop Color="#A7D9F5" Offset="1"/>
        </LinearGradientBrush>
        <SolidColorBrush x:Key="TabItemSelectedBackground" Color="#F9F9F9"/>
        <SolidColorBrush x:Key="TabItemHotBorderBrush" Color="#3C7FB1"/>
        <SolidColorBrush x:Key="TabItemDisabledBackground" Color="#F4F4F4"/>
        <SolidColorBrush x:Key="TabItemDisabledBorderBrush" Color="#FFC9C7BA"/>
        <Style x:Key="TabItemStyle1" TargetType="{x:Type TabItem}">
            <Setter Property="FocusVisualStyle" Value="{StaticResource TabItemFocusVisual}"/>
            <Setter Property="Foreground" Value="Black"/>
            <Setter Property="Padding" Value="6,1,6,1"/>
            <Setter Property="BorderBrush" Value="{StaticResource TabControlNormalBorderBrush}"/>
            <Setter Property="Background" Value="{StaticResource ButtonNormalBackground}"/>
            <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
            <Setter Property="VerticalContentAlignment" Value="Stretch"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TabItem}">
                        <Grid SnapsToDevicePixels="true">
                            <Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="1,1,1,0" Background="{TemplateBinding Background}" Padding="{TemplateBinding Padding}">
                                <ContentPresenter x:Name="Content" ContentSource="Header" HorizontalAlignment="{Binding HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{Binding VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
                            </Border>
                        </Grid>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsMouseOver" Value="true">
                                <Setter Property="Background" TargetName="Bd" Value="{StaticResource TabItemHotBackground}"/>
                            </Trigger>
                            <Trigger Property="IsSelected" Value="true">
                                <Setter Property="Panel.ZIndex" Value="1"/>
                                <Setter Property="Background" TargetName="Bd" Value="{StaticResource TabItemSelectedBackground}"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="false"/>
                                    <Condition Property="IsMouseOver" Value="true"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource TabItemHotBorderBrush}"/>
                            </MultiTrigger>
                            <Trigger Property="TabStripPlacement" Value="Bottom">
                                <Setter Property="BorderThickness" TargetName="Bd" Value="1,0,1,1"/>
                            </Trigger>
                            <Trigger Property="TabStripPlacement" Value="Left">
                                <Setter Property="BorderThickness" TargetName="Bd" Value="1,1,0,1"/>
                            </Trigger>
                            <Trigger Property="TabStripPlacement" Value="Right">
                                <Setter Property="BorderThickness" TargetName="Bd" Value="0,1,1,1"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="true"/>
                                    <Condition Property="TabStripPlacement" Value="Top"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Margin" Value="-2,-2,-2,-1"/>
                                <Setter Property="Margin" TargetName="Content" Value="0,0,0,1"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="true"/>
                                    <Condition Property="TabStripPlacement" Value="Bottom"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Margin" Value="-2,-1,-2,-2"/>
                                <Setter Property="Margin" TargetName="Content" Value="0,1,0,0"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="true"/>
                                    <Condition Property="TabStripPlacement" Value="Left"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Margin" Value="-2,-2,-1,-2"/>
                                <Setter Property="Margin" TargetName="Content" Value="0,0,1,0"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="true"/>
                                    <Condition Property="TabStripPlacement" Value="Right"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Margin" Value="-1,-2,-2,-2"/>
                                <Setter Property="Margin" TargetName="Content" Value="1,0,0,0"/>
                            </MultiTrigger>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Background" TargetName="Bd" Value="{StaticResource TabItemDisabledBackground}"/>
                                <Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource TabItemDisabledBorderBrush}"/>
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>