<Style x:Key="comboxStyle2" TargetType="{x:Type ComboBox}">
<Setter Property="ItemContainerStyle">
<Setter.Value>
<Style TargetType="ComboBoxItem">
<Setter Property="Height" Value="30"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBoxItem}">
<Grid Height="{TemplateBinding Height}" Width="{TemplateBinding Width}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="20" MaxWidth="30" />
</Grid.ColumnDefinitions>
<Border x:Name="_borderbg" Background="Transparent"/>
<TextBlock Margin="3 0 3 0" VerticalAlignment="Center" x:Name="_txt" Foreground="#333" Text="{Binding Content,RelativeSource={RelativeSource TemplatedParent}}"/>
<Button x:Name="_button" Grid.Column="1" VerticalAlignment="Center" VerticalContentAlignment="Top" HorizontalAlignment="Right" Background="Transparent" BorderThickness="0" Width="20" Height="30" Cursor="Hand" Content="×" Command="{Binding DataContext.DeleteCommand, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=Window}}" CommandParameter="{Binding ElementName=_txt,Path=Text}"/>
<Border x:Name="_border" Background="White" Opacity="0"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsSelected" Value="true">
<Setter TargetName="_borderbg" Property="Background" Value="{StaticResource ComboBoxSelectdBackground}" />
<Setter TargetName="_txt" Property="Foreground" Value="{StaticResource ComboBoxSelectedForeground}"/>
<Setter TargetName="_button" Property="Background" Value="{StaticResource ComboBoxSelectdBackground}"/>
</Trigger>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsSelected" Value="false"/>
<Condition Property="IsMouseOver" Value="true"/>
</MultiTrigger.Conditions>
<Setter TargetName="_borderbg" Property="Background" Value="{StaticResource ComboBoxMouseOverBackground}" />
<Setter TargetName="_txt" Property="Foreground" Value="{StaticResource ComboBoxMouseOverForegrond}"/>
<Setter TargetName="_button" Property="Background" Value="{StaticResource ComboBoxMouseOverBackground}"/>
</MultiTrigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Setter.Value>
</Setter>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ComboBox}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="0.7*"/>
<ColumnDefinition Width="0.3*" MaxWidth="30"/>
</Grid.ColumnDefinitions>
<Border Grid.Column="0" Grid.ColumnSpan="2" BorderThickness="1" BorderBrush="{TemplateBinding BorderBrush}" CornerRadius="1,0,0,1"/>
<ContentPresenter HorizontalAlignment="Left" Margin="3,3,0,3" x:Name="ContentSite" VerticalAlignment="Center" Content="{TemplateBinding SelectionBoxItem}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}" IsHitTestVisible="False"/>
<!--ToggleButton 已数据绑定到 ComboBox 本身以切换 IsDropDownOpen-->
<ToggleButton Grid.Column="0" Grid.ColumnSpan="2" Template="{StaticResource ComboBoxToggleButton}" x:Name="ToggleButton" Focusable="false" IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Press"/>
<!--必须将 TextBox 命名为 PART_EditableTextBox，否则 ComboBox 将无法识别它-->
<TextBox Visibility="Hidden" BorderThickness="0" Margin="2 0 0 0" x:Name="PART_EditableTextBox" VerticalAlignment="Center" Focusable="True" Background="Transparent" IsReadOnly="{TemplateBinding IsReadOnly}"/>
<!--Popup 可显示 ComboBox 中的项列表。IsOpen 已数据绑定到通过 ComboBoxToggleButton 来切换的 IsDropDownOpen-->
<Popup IsOpen="{TemplateBinding IsDropDownOpen}" Placement="Bottom" x:Name="Popup" Focusable="False" AllowsTransparency="True" PopupAnimation="Slide">
<Grid MaxHeight="150" MinWidth="{TemplateBinding ActualWidth}" x:Name="DropDown" SnapsToDevicePixels="True">
<Border x:Name="DropDownBorder" BorderBrush="#e8e8e8" BorderThickness="1 0 1 1"/>
<ScrollViewer Margin="1" SnapsToDevicePixels="True" HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto" CanContentScroll="True">
<!--StackPanel 用于显示子级，方法是将 IsItemsHost 设置为 True-->
<StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" Background="White"/>
</ScrollViewer>
</Grid>
</Popup>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsEditable" Value="true">
<Setter TargetName="PART_EditableTextBox" Property="Visibility" Value="Visible" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
主要是通过RelativeSource 进行 DataContext 查找，进而进行绑定。
Command="{Binding DataContext.DeleteCommand, RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=Window}}"
AncestorType的值取决于父窗体所在是WIndow还是UserControl