将CollectionViewSource与GroupDescriptions一起使用时的ListBox ScrollI

短版本

我想在更改选择时将ListBox项目滚动到视图中。

长版本

我有一个带有ItemsSource的ListBox绑定到带有GroupDescription的CollectionViewSource，如下例所示。

<Window.Resources>
    <CollectionViewSource x:Key="AnimalsView" Source="{Binding Source={StaticResource Animals}, Path=AnimalList}">
        <CollectionViewSource.GroupDescriptions>
            <PropertyGroupDescription PropertyName="Category"/>
        </CollectionViewSource.GroupDescriptions>
    </CollectionViewSource>  
</Window.Resources>
<ListBox x:Name="AnimalsListBox"ItemsSource="{Binding Source={StaticResource AnimalsView}}" ItemTemplate="{StaticResource AnimalTemplate}" SelectionChanged="ListBox_SelectionChanged">
    <ListBox.GroupStyle>
        <GroupStyle HeaderTemplate="{StaticResource CategoryTemplate}" />
    </ListBox.GroupStyle>
</ListBox>

代码隐藏文件中有一个SelectionChanged事件。

public List<Animal> Animals { get; set; }
private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    ListBox control = (ListBox)sender;
    control.ScrollIntoView(control.SelectedItem);
}

现在。如果我将AnimalsListBox.SelectedItem设置为当前不可见的项目，我希望它在视图中滚动。这就是它变得棘手的地方，因为ListBox是组(IsGrouped属性是true(，所以对ScrollIntoView的调用失败。

System.Windows.Controls.ListBox通过反射器。注意OnBringItemIntoView中的base.IsGrouping。

public void ScrollIntoView(object item)
{
    if (base.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
    {
        this.OnBringItemIntoView(item);
    }
    else
    {
        base.Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new DispatcherOperationCallback(this.OnBringItemIntoView), item);
    }
}
private object OnBringItemIntoView(object arg)
{
    FrameworkElement element = base.ItemContainerGenerator.ContainerFromItem(arg) as FrameworkElement;
    if (element != null)
    {
        element.BringIntoView();
    }
    else if (!base.IsGrouping && base.Items.Contains(arg))
    {
        VirtualizingPanel itemsHost = base.ItemsHost as VirtualizingPanel;
        if (itemsHost != null)
        {
            itemsHost.BringIndexIntoView(base.Items.IndexOf(arg));
        }
    }
    return null;
}

问题

1. 有人能解释为什么使用分组时不起作用吗？
   • ItemContainerGenerator.ContainerFromItem总是返回null，即使它的状态表示所有容器都已生成
2. 当使用分组时，我如何实现滚动到视图中

private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    ListBox control = (ListBox)sender;
    if (control.IsGrouping)
    {
         if (control.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
              Dispatcher.BeginInvoke(DispatcherPriority.Render, new Action(DelayedBringIntoView));
         else
              control.ItemContainerGenerator.StatusChanged += ItemContainerGenerator_StatusChanged;
    }
    else
        control.ScrollIntoView(control.SelectedItem);
}
private void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)
{
    if (ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)
        return;
    ItemContainerGenerator.StatusChanged -= ItemContainerGenerator_StatusChanged;
    Dispatcher.BeginInvoke(DispatcherPriority.Render, new Action(DelayedBringIntoView));
}
private void DelayedBringIntoView()
{
    var item = ItemContainerGenerator.ContainerFromItem(SelectedItem) as ListBoxItem;
    if (item != null)
        item.BringIntoView();
}