WPF - C# - ComboBox/ComboBoxItem: How to stretch text to fill combobox area

Question

I am programmatically adding ComboBoxes and ComboBox Items. I have a custom ComboBox Style implemented. Everything is fine except the text for each combo box item will not stretch to fill the combobox area. I can get this automatic stretching to work fine with labels and buttons using this bit of XAML in the Custom Style of the button and label controls but it does not have any effect in the ComboBoxItem control.

<Setter Property="ContentTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <Viewbox Stretch="Fill">
                            <ContentPresenter Content="{TemplateBinding Content}"/>
                        </Viewbox>
                    </DataTemplate>
                </Setter.Value>
            </Setter>

Since I am not adding the ComboBoxes in XAML, a solution that involves adding a custom TextBlock will not work (unless it is done dynamically/programmatically). The solution has to either be done in the custom style, or done programmatically in the code behind.

<!--ComboBox Template-->
        <ControlTemplate x:Key="ComboBoxTemplate" TargetType="{x:Type ComboBox}">
            <Grid x:Name="templateRoot" SnapsToDevicePixels="true">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="*"/>
                    <ColumnDefinition MinWidth="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" Width="0"/>
                </Grid.ColumnDefinitions>
                <Popup x:Name="PART_Popup" AllowsTransparency="true" Grid.ColumnSpan="2" IsOpen="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Margin="1" 
                       PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}" Placement="Bottom">
                    <Themes:SystemDropShadowChrome x:Name="shadow" Color="Transparent" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{Binding ActualWidth, ElementName=templateRoot}">
                        <Border x:Name="dropDownBorder" BorderBrush="{StaticResource backgroundColorBrush}" BorderThickness="0" Background="{StaticResource backgroundColorBrush}">
                            <ScrollViewer x:Name="DropDownScrollViewer">
                                <Grid x:Name="grid" RenderOptions.ClearTypeHint="Enabled">
                                    <Canvas x:Name="canvas" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="0">
                                        <Rectangle x:Name="opaqueRect" Fill="{StaticResource backgroundColorBrush}"
                                                   Width="{Binding ActualWidth, ElementName=dropDownBorder}"/>
                                    </Canvas>
                                    <ItemsPresenter x:Name="ItemsPresenter" KeyboardNavigation.DirectionalNavigation="Contained" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                                </Grid>
                            </ScrollViewer>
                        </Border>
                    </Themes:SystemDropShadowChrome>
                </Popup>
                <ToggleButton x:Name="toggleButton" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.ColumnSpan="2" 
                              IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Style="{StaticResource ComboBoxToggleButton}"/>
                <ContentPresenter x:Name="contentPresenter" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" 
                                  Content="{TemplateBinding SelectionBoxItem}" ContentStringFormat="{TemplateBinding SelectionBoxItemStringFormat}" HorizontalAlignment="Left" 
                                  IsHitTestVisible="false" Margin="0, 0, 0, 0" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="Center"/>
            </Grid>
            <ControlTemplate.Triggers>
                <!--<Trigger Property="HasItems" Value="false">
                    <Setter Property="Height" TargetName="dropDownBorder" Value="{StaticResource height}"/>
                </Trigger>-->
                <MultiTrigger>
                    <MultiTrigger.Conditions>
                        <Condition Property="IsGrouping" Value="true"/>
                        <Condition Property="VirtualizingPanel.IsVirtualizingWhenGrouping" Value="false"/>
                    </MultiTrigger.Conditions>
                    <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
                </MultiTrigger>
                <Trigger Property="ScrollViewer.CanContentScroll" SourceName="DropDownScrollViewer" Value="false">
                    <Setter Property="Canvas.Top" TargetName="opaqueRect" Value="{Binding VerticalOffset, ElementName=DropDownScrollViewer}"/>
                    <Setter Property="Canvas.Left" TargetName="opaqueRect" Value="{Binding HorizontalOffset, ElementName=DropDownScrollViewer}"/>
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>
        <!--ComboBox-->
        <Style TargetType="{x:Type ComboBox}">
            <Setter Property="Background" Value="{StaticResource backgroundColorBrush}"/>
            <Setter Property="BorderBrush" Value="{StaticResource backgroundColorBrush}"/>
            <Setter Property="Foreground" Value="{StaticResource textColorBrush}"/>
            <Setter Property="Width" Value="Auto"/>
            <Setter Property="FontSize" Value="30"/>
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="VerticalAlignment" Value="Stretch"/>
            <Setter Property="HorizontalAlignment" Value="Stretch"/>
            <Setter Property="VerticalContentAlignment" Value="Stretch"/>
            <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
            <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
            <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
            <Setter Property="Padding" Value="0,0,0,0"/>
            <Setter Property="ScrollViewer.CanContentScroll" Value="False"/>
            <Setter Property="ScrollViewer.PanningMode" Value="None"/>
            <Setter Property="Stylus.IsFlicksEnabled" Value="False"/>
            <Setter Property="Template" Value="{StaticResource ComboBoxTemplate}"/>

            <Style.Triggers>
                <Trigger Property="IsEditable" Value="true">
                    <Setter Property="IsTabStop" Value="false"/>
                    <Setter Property="Padding" Value="2"/>
                </Trigger>
            </Style.Triggers>
        </Style>
        <!--ComboBox Item-->
        <Style TargetType="{x:Type ComboBoxItem}">
            <Setter Property="SnapsToDevicePixels" Value="True"/>
            <Setter Property="Padding" Value="0,0"/>
            <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
            <Setter Property="VerticalContentAlignment" Value="Stretch"/>
            <Setter Property="VerticalAlignment" Value="Stretch"/>
            <Setter Property="HorizontalAlignment" Value="Stretch"/>
            <Setter Property="Background" Value="Transparent"/>
            <Setter Property="BorderBrush" Value="Transparent"/>
            <!--<Setter Property="FontSize" Value="Auto"/>-->
            <!--<Setter Property="Height" Value="{StaticResource height}"/>-->
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="ContentTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <Viewbox Stretch="Uniform">
                            <ContentPresenter Content="{TemplateBinding Content}"/>
                        </Viewbox>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type ComboBoxItem}">
                        <Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="0" 
                                SnapsToDevicePixels="true">
                            <ContentPresenter HorizontalAlignment="Stretch" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="Stretch"/>
                        </Border>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsEnabled" Value="False">
                                <Setter Property="TextElement.Foreground" TargetName="Bd" Value="{StaticResource textColorBrush}"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="False"/>
                                    <Condition Property="IsMouseOver" Value="True"/>
                                    <Condition Property="IsKeyboardFocused" Value="False"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Background" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                                <Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="True"/>
                                    <Condition Property="IsMouseOver" Value="False"/>
                                    <Condition Property="IsKeyboardFocused" Value="True"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Background" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                                <Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="True"/>
                                    <Condition Property="IsMouseOver" Value="True"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Background" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                                <Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="True"/>
                                    <Condition Property="IsMouseOver" Value="False"/>
                                    <Condition Property="IsKeyboardFocused" Value="False"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Background" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                                <Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="False"/>
                                    <Condition Property="IsMouseOver" Value="False"/>
                                    <Condition Property="IsKeyboardFocused" Value="True"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="False"/>
                                    <Condition Property="IsMouseOver" Value="True"/>
                                    <Condition Property="IsKeyboardFocused" Value="True"/>
                                </MultiTrigger.Conditions>
                                <Setter Property="Background" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                                <Setter Property="BorderBrush" TargetName="Bd" Value="{StaticResource highlightedColorBrush}"/>
                            </MultiTrigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <!--Used by CheckBoxStyle1-->
        <Style x:Key="OptionMarkFocusVisual">
            <Setter Property="Control.Template">
                <Setter.Value>
                    <ControlTemplate>
                        <Rectangle Margin="14,0,0,0" SnapsToDevicePixels="true" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

Try with ComboBox's HorizontalContentAlignement & VerticalContentAlignment set to Stretch — nkoniishvt
– nkoniishvt, Commented Dec 28, 2015 at 12:19
@john can you please publish the code where you construct the comboitem? — Ilan
– Ilan, Commented Dec 28, 2015 at 12:37
@John can you please publish the custom ComboBox style XAML? — Luke Le
– Luke Le, Commented Dec 28, 2015 at 16:06

nkoniishvt · Accepted Answer · 2015-12-28 13:13:52Z

2

ComboBox's HorizontalContentAlignment defaults to Left and VerticalContentAlignment defaults to Top. Set them both to Stretch.

answered Dec 28, 2015 at 13:13

nkoniishvt

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3 Comments

John Over a year ago

I have them set to stretch already. That makes the combo box stretch to fill the parent container but does nothing to the text in the combo box

nkoniishvt Over a year ago

You're talking about Verticalalignment, i'm talking about VerticalContentAlignment. You have it set to stretch in your ComboBoxItem style but not in your ComboBox style

John Over a year ago

I had those two also set to stretch. The problem was that it was being overridden further down in the custom ComboBoxItem style. Now the comboboxItem font stretches, but once it is selected it is tiny again. The ContentTemplate property code (in my original post) works in a ComboBoxItem style, but is not valid/allowed in the ComboBox custom style. Is there an equivalent to get the selected item to also stretch?

Radin Gospodinov · Accepted Answer · 2015-12-29 10:42:13Z

0

Add this implicit style in your content template:

<Viewbox Stretch="Fill">
            <Viewbox.Resources>
                <Style TargetType="TextBlock">
                    <Setter Property="HorizontalAlignment" Value="Stretch"/>
                    <Setter Property="TextAlignment" Value="Justify"></Setter>
                </Style>
....

answered Dec 29, 2015 at 10:42

Radin Gospodinov

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