BeWoPlaner/BeWo.Styles/ControlStyles/NullItemComboBoxStyles.xaml

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:Microsoft_Windows_Themes="clr-namespace:Microsoft.Windows.Themes;assembly=PresentationFramework.Aero"
    xmlns:uc="clr-namespace:BeWo.Controls;assembly=BeWo.Controls">

    <!--  NullItemComboBox  -->
    <Style x:Key="PrimaryNullItemComboBox" TargetType="uc:NullItemComboBox">
        <Setter Property="Margin" Value="3" />
        <Setter Property="Height" Value="23" />
        <Setter Property="FocusVisualStyle" Value="{DynamicResource ComboBoxFocusVisual}" />
        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}" />
        <Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}" />
        <Setter Property="BorderBrush" Value="{DynamicResource TextBoxBorderBrush}" />
        <Setter Property="BorderThickness" Value="1" />
        <Setter Property="Padding" Value="1" />
        <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto" />
        <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto" />
        <Setter Property="ScrollViewer.CanContentScroll" Value="true" />
        <Setter Property="VerticalContentAlignment" Value="Center" />
        <Setter Property="ItemTemplate">
            <Setter.Value>
                <DataTemplate>
                    <TextBlock Text="{Binding Path=.}" TextWrapping="NoWrap" />
                </DataTemplate>
            </Setter.Value>
        </Setter>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type uc:NullItemComboBox}">
                    <Grid SnapsToDevicePixels="true">
                        <Border
                            x:Name="Bd"
                            Padding="1"
                            Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                            <Grid Grid.IsSharedSizeScope="true">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="1" />
                                    <ColumnDefinition Width="*" />
                                    <ColumnDefinition Width="Auto" SharedSizeGroup="ComboBoxButton" />
                                </Grid.ColumnDefinitions>
                                <Border
                                    x:Name="SelectedItemBorder"
                                    Grid.ColumnSpan="2"
                                    Margin="2,1,20,1">
                                    <ContentPresenter
                                        Margin="3,0"
                                        HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                        VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                                        Content="{TemplateBinding SelectionBoxItem}"
                                        ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
                                        ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
                                        SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
                                </Border>
                                <ToggleButton
                                    Grid.Column="0"
                                    Grid.ColumnSpan="3"
                                    IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"
                                    Style="{DynamicResource ComboBoxTransparentButtonStyle}" />
                                <Label
                                    x:Name="label_nullText"
                                    Grid.Column="0"
                                    Grid.ColumnSpan="2"
                                    Margin="5,3,20,3"
                                    Padding="0"
                                    HorizontalAlignment="Left"
                                    VerticalAlignment="Center"
                                    Content="{TemplateBinding NullText}"
                                    IsHitTestVisible="False"
                                    Visibility="Hidden" />
                            </Grid>
                        </Border>
                        <Popup
                            x:Name="PART_Popup"
                            AllowsTransparency="true"
                            Focusable="false"
                            IsOpen="{Binding Path=IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}"
                            Placement="Bottom"
                            PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}">
                            <Microsoft_Windows_Themes:SystemDropShadowChrome
                                x:Name="Shdw"
                                MinWidth="{TemplateBinding ActualWidth}"
                                MaxHeight="{TemplateBinding MaxDropDownHeight}"
                                Color="Transparent">
                                <Border
                                    x:Name="DropDownBorder"
                                    Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"
                                    BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}"
                                    BorderThickness="1">
                                    <ScrollViewer>
                                        <ItemsPresenter KeyboardNavigation.DirectionalNavigation="Contained" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
                                    </ScrollViewer>
                                </Border>
                            </Microsoft_Windows_Themes:SystemDropShadowChrome>
                        </Popup>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <MultiTrigger>
                            <MultiTrigger.Conditions>
                                <Condition Property="IsSelectionBoxHighlighted" Value="true" />
                                <Condition Property="IsDropDownOpen" Value="false" />
                            </MultiTrigger.Conditions>
                            <Setter Property="Foreground" Value="#FF000000" />
                        </MultiTrigger>
                        <Trigger Property="IsSelectionBoxHighlighted" Value="true">
                            <Setter TargetName="SelectedItemBorder" Property="Background" Value="{DynamicResource ControlSelectedBackgroundBrush}" />
                        </Trigger>
                        <Trigger SourceName="PART_Popup" Property="HasDropShadow" Value="true">
                            <Setter TargetName="Shdw" Property="Margin" Value="0,0,5,5" />
                            <Setter TargetName="Shdw" Property="Color" Value="#71000000" />
                        </Trigger>
                        <Trigger Property="HasItems" Value="false">
                            <Setter TargetName="DropDownBorder" Property="MinHeight" Value="95" />
                        </Trigger>
                        <Trigger Property="IsEnabled" Value="false">
                            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" />
                            <Setter TargetName="Bd" Property="Background" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}" />
                        </Trigger>
                        <Trigger Property="IsGrouping" Value="true">
                            <Setter Property="ScrollViewer.CanContentScroll" Value="false" />
                        </Trigger>
                        <Trigger Property="SelectedItem" Value="{x:Null}">
                            <Setter TargetName="label_nullText" Property="Visibility" Value="Visible" />
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Style.Triggers>
            <Trigger Property="IsEditable" Value="true">
                <Setter Property="IsTabStop" Value="false" />
                <Setter Property="Padding" Value="0,1" />
                <Setter Property="Template" Value="{DynamicResource ComboBoxEditableTemplate}" />
            </Trigger>
        </Style.Triggers>
    </Style>

    <Style
        x:Key="EnumTranslationNullItemComboBox"
        BasedOn="{StaticResource PrimaryNullItemComboBox}"
        TargetType="{x:Type uc:NullItemComboBox}">
        <Setter Property="ItemTemplate" Value="{DynamicResource ListItemView}" />
        <Setter Property="HorizontalAlignment" Value="Stretch" />
        <Setter Property="MaxWidth" Value="400" />
    </Style>
</ResourceDictionary>