将CollectionViewSource与GroupDescriptions结合使用时ListBox ScrollIntoView(即IsGrouping == True)

Question

精简版

我想ListBox在选择更改时将项目滚动到视图中.

长版

我有一个ListBox与所述ItemsSource绑定到一个CollectionViewSource具有GroupDescription,按照下面的例子.

<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>

SelectionChanged代码隐藏文件中有一个事件.

public List<Animal> Animals { get; set; }

private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    ListBox control = (ListBox)sender;
    control.ScrollIntoView(control.SelectedItem);
}

现在.如果我将其设置AnimalsListBox.SelectedItem为当前不可见的项目,我希望将其滚动到视图中.这就是它变得棘手的地方,因为ListBox群组(IsGrouped属性true)是ScrollIntoView失败的调用.

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

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. 谁能解释为什么它不工作时使用的分组？
   • 将ItemContainerGenerator.ContainerFromItem始终返回null,即使它已经产生的所有集装箱状态的状态.
2. 使用分组时如何实现滚动视图？

Answer 1

我找到了解决问题的方法.我确信我不是第一个遇到这个问题的人,所以我继续搜索StackOverflow的解决方案,我偶然发现了David 关于ItemContainerGenerator如何使用分组列表的答案.

大卫的解决办法是推迟访问ItemContainerGenerator,直到之后的渲染过程.

我已经实现了这个解决方案,我将详细介绍一些更改.

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();
}

变化:

• 只使用ItemContainerGenerator时,它的做法IsGrouping是true,否则继续使用默认ScrollIntoView.
• 检查是否ItemContainerGenerator准备就绪,如果是,则调度操作,否则监听ItemContainerGenerator状态改变.这很重要,好像它已准备就绪,然后StatusChanged事件永远不会触发.