如何实施ZIndex？

Question

我有一个ListBox，填充了CollectionViewSource，以便将项目分组。

        <ListBox
            x:Name="Positions"
            Margin="10,0,0,0"
            BorderThickness="0"
            IsSynchronizedWithCurrentItem="False"
            ItemsSource="{Binding Source={StaticResource cvsItems}}"
            SelectedItem="{Binding SelectedItem}"
            SelectionMode="Extended">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <StackPanel Orientation="Horizontal">
                            <Separator
                                Margin="-8,-19,10,11"
                                SnapsToDevicePixels="True"
                                Style="{StaticResource {x:Static ToolBar.SeparatorStyleKey}}"
                                Visibility="{Binding IsPartOfAverageGroup, Converter={StaticResource boolToVisibilityConverter}}" Grid.ZIndex="1"/>
                            <Separator
                                Width="40"
                                Margin="-10,0,8,0"
                                SnapsToDevicePixels="True"
                                Visibility="{Binding IsPartOfAverageGroup, Converter={StaticResource boolToVisibilityConverter}}" />
                            <TextBlock Text="{Binding Name}" />
                            <Image
                                Height="12"
                                Margin="5,0,0,0"
                                Source="/Images/2017/Editable.png">
                                <Image.Style>
                                    <Style TargetType="Image">
                                        <Style.Triggers>
                                            <DataTrigger Binding="{Binding IsReadOnly}" Value="True">
                                                <Setter Property="Visibility" Value="Collapsed" />
                                            </DataTrigger>
                                        </Style.Triggers>
                                    </Style>
                                </Image.Style>
                            </Image>
                        </StackPanel>
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
            <ListBox.ItemContainerStyle>
                <Style BasedOn="{StaticResource ListBoxItemStyle}" TargetType="ListBoxItem">
                    <Setter Property="IsSelected" Value="{Binding Mode=TwoWay, Path=IsSelected}" />
                </Style>
            </ListBox.ItemContainerStyle>
            <ListBox.GroupStyle>
                <GroupStyle>
                    <GroupStyle.HeaderTemplate>
                        <DataTemplate>
                            <StackPanel Orientation="Horizontal">
                                <Ellipse
                                    Width="8"
                                    Height="8"
                                    Margin="1,0,0,0"
                                    Grid.ZIndex="10000"
                                    Fill="#0589D1" />
                                <Button
                                    Margin="15,0,0,0"
                                    HorizontalContentAlignment="Left"
                                    cal:Message.Attach="SelectAverageGroup($dataContext)"
                                    Content="{Binding Name}" />
                                <StackPanel.Style>
                                    <Style TargetType="StackPanel">
                                        <Style.Triggers>
                                            <DataTrigger Binding="{Binding Name}" Value="">
                                                <Setter Property="Visibility" Value="Collapsed" />
                                            </DataTrigger>
                                        </Style.Triggers>
                                    </Style>
                                </StackPanel.Style>
                            </StackPanel>
                        </DataTemplate>
                    </GroupStyle.HeaderTemplate>
                </GroupStyle>
            </ListBox.GroupStyle>
        </ListBox>

这是我的CollectionViewSource：

<UserControl.Resources>
    <CollectionViewSource x:Key="cvsItems" Source="{Binding Items}">
        <CollectionViewSource.GroupDescriptions>
            <PropertyGroupDescription PropertyName="AverageGroup.Name" />
        </CollectionViewSource.GroupDescriptions>
    </CollectionViewSource>
</UserControl.Resources>

您可以在DataTemplate中看到ListBox，我想绘制连接Group Header和分组项的行。这是一张图片来澄清：

我希望蓝色圆圈位于灰线前面，而不是相反。我试图将垂直灰色分隔符的ZIndex和蓝色圆圈的ZIndex设置为1000，以便后者位于前面。我在这做错了什么？感谢您对此的任何帮助。