无法获得列表视图组展开头显示

我正在尝试在WPF列表视图中分组项目列表-其工作良好，但我无法获得扩展头显示。

我设置组的样式如下:

<!--  Styles the groups  -->
            <ListView.GroupStyle>
                <GroupStyle>
                    <GroupStyle.ContainerStyle>
                        <Style TargetType="{x:Type GroupItem}">
                            <Setter Property="Template">
                                <Setter.Value>
                                    <ControlTemplate>
                                        <Expander BorderBrush="LightBlue"
                                            BorderThickness="1"
                                            IsExpanded="True"
                                                  Name="groupExpander"
                                            Header="{Binding Family}">
                                            <ItemsPresenter />
                                        </Expander>
                                    </ControlTemplate>
                                </Setter.Value>
                            </Setter>
                        </Style>
                    </GroupStyle.ContainerStyle>
                </GroupStyle>
            </ListView.GroupStyle>

和列表视图项源绑定在后面的代码中:

//group by shape family
CollectionView view = (CollectionView)CollectionViewSource.GetDefaultView(GetShapes());
PropertyGroupDescription groupDescription = new PropertyGroupDescription("Family");
view.GroupDescriptions.Add(groupDescription);
ImagesListView.ItemsSource = view;

最后，我绑定到这个对象的列表(我想在家庭字段上分组，这个字符串出现在组头:

public class Shape
{
        public int ID { get; private set; }
        public byte[] Image { get; private set; }
        public string Description { get; private set; }
        public string Family { get; private set; }

}

我没有做什么或做错了什么?

Header="{Binding Family}"

Header="{Binding Name}"