c# - 如何在 ListView 的组标题中保存 IsExpanded 状态

Question

我有一个相当棘手的问题:

我正在使用 ListView 控件，其中 ItemsSource 设置为 CollectionViewSource，包括 PropertyGroupDescription 以对 ListView 元素进行分组。 CollectionViewSource 看起来像这样:

<CollectionViewSource x:Key="ListViewObjects">
   <CollectionViewSource.Source>
      <Binding Path="CurrentListViewData"/>
   </CollectionViewSource.Source>
   <CollectionViewSource.GroupDescriptions>
      <PropertyGroupDescription PropertyName="ObjectType" />
   </CollectionViewSource.GroupDescriptions>
</CollectionViewSource>

在 ListView 中，我使用如下自定义组标题:

<ListView.GroupStyle>
   <GroupStyle>
      <GroupStyle.ContainerStyle>
         <Style TargetType="{x:Type GroupItem}">
            <Setter Property="Margin" Value="5"/>
            <Setter Property="Template">
               <Setter.Value>
                  <ControlTemplate TargetType="{x:Type GroupItem}">
                     <Expander IsExpanded="True">
                        <Expander.Header>
                           <DockPanel>
                              <TextBlock Text="{Binding Path=Items[0].ObjectType />
                           </DockPanel>
                        </Expander.Header>
                        <Expander.Content>
                           <ItemsPresenter />
                        </Expander.Content>
                     </Expander>
                  </ControlTemplate>
               </Setter.Value>
            </Setter>
         </Style>
      </GroupStyle.ContainerStyle>
   </GroupStyle>
</ListView.GroupStyle>

如您所见，Expander 的 IsExpanded 属性设置为 true。这意味着每当 ListView 刷新时，所有 Expander 控件都会展开。

但是我确实想保存每个 Expander 的最后状态。我还没有想出一种方法来保存每个 ObjectType 的扩展器状态列表。我正在尝试使用绑定(bind)的 HashTable 和 Converter，但我未能将 ObjectType 作为 ConverterParameter 提供，因为它始终作为字符串传递。但这可能不是解决方案。

有人可以给我一个解决方案的提示或想法吗？ :)

Answer 1

如评论中所述，接受的答案是错误的。我编写了以下实现所需功能的行为:

public class PersistGroupExpandedStateBehavior : Behavior<Expander>
{
    #region Static Fields

    public static readonly DependencyProperty GroupNameProperty = DependencyProperty.Register(
        "GroupName", 
        typeof(object), 
        typeof(PersistGroupExpandedStateBehavior), 
        new PropertyMetadata(default(object)));

    private static readonly DependencyProperty ExpandedStateStoreProperty =
        DependencyProperty.RegisterAttached(
            "ExpandedStateStore", 
            typeof(IDictionary<object, bool>), 
            typeof(PersistGroupExpandedStateBehavior), 
            new PropertyMetadata(default(IDictionary<object, bool>)));

    #endregion

    #region Public Properties

    public object GroupName
    {
        get
        {
            return (object)this.GetValue(GroupNameProperty);
        }

        set
        {
            this.SetValue(GroupNameProperty, value);
        }
    }

    #endregion

    #region Methods

    protected override void OnAttached()
    {
        base.OnAttached();

        bool? expanded = this.GetExpandedState();

        if (expanded != null)
        {
            this.AssociatedObject.IsExpanded = expanded.Value;
        }

        this.AssociatedObject.Expanded += this.OnExpanded;
        this.AssociatedObject.Collapsed += this.OnCollapsed;
    }

    protected override void OnDetaching()
    {
        this.AssociatedObject.Expanded -= this.OnExpanded;
        this.AssociatedObject.Collapsed -= this.OnCollapsed;

        base.OnDetaching();
    }

    private ItemsControl FindItemsControl()
    {
        DependencyObject current = this.AssociatedObject;

        while (current != null && !(current is ItemsControl))
        {
            current = VisualTreeHelper.GetParent(current);
        }

        if (current == null)
        {
            return null;
        }

        return current as ItemsControl;
    }

    private bool? GetExpandedState()
    {
        var dict = this.GetExpandedStateStore();

        if (!dict.ContainsKey(this.GroupName))
        {
            return null;
        }

        return dict[this.GroupName];
    }

    private IDictionary<object, bool> GetExpandedStateStore()
    {
        ItemsControl itemsControl = this.FindItemsControl();

        if (itemsControl == null)
        {
            throw new Exception(
                "Behavior needs to be attached to an Expander that is contained inside an ItemsControl");
        }

        var dict = (IDictionary<object, bool>)itemsControl.GetValue(ExpandedStateStoreProperty);

        if (dict == null)
        {
            dict = new Dictionary<object, bool>();
            itemsControl.SetValue(ExpandedStateStoreProperty, dict);
        }

        return dict;
    }

    private void OnCollapsed(object sender, RoutedEventArgs e)
    {
        this.SetExpanded(false);
    }

    private void OnExpanded(object sender, RoutedEventArgs e)
    {
        this.SetExpanded(true);
    }

    private void SetExpanded(bool expanded)
    {
        var dict = this.GetExpandedStateStore();

        dict[this.GroupName] = expanded;
    }

    #endregion
}

它将字典附加到包含的 ItemsControl，它保存每个组项目的展开状态。这将是持久的，即使控件中的项目发生变化也是如此。

用法:

<Expander>
    <i:Interaction.Behaviors>
        <behaviors:PersistGroupExpandedStateBehavior GroupName="{Binding Name}" />
    </i:Interaction.Behaviors>
    ...
</Expander>