短版
当选择更改时,我想将ListBox项目滚动到视图中.
长版
我有一个ListBox,ItemsSource绑定到一个GroupViewSource与一个GroupDescription,如下面的例子.
<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>
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.这是它变得棘手的地方,因为ListBox是组(IsGrouped属性为true),对ScrollIntoView的调用失败.
System.Windows.Controls.ListBox通过反射器.注意在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
>任何人都可以解释为什么在使用分组时不起作用？
> ItemContainerGenerator.ContainerFromItem始终返回null,即使状态表示已经生成了所有容器.
>使用分组时如何实现滚动浏览？
解决方法
我找到了解决我的问题的办法.我确信我不是第一个打这个问题的人,所以我继续搜索StackOverflow的解决方案,而我在这个答案中偶然发现了David
about how ItemContainerGenerator works with a grouped list.
David的解决方案是延迟访问ItemContainerGenerator,直到渲染过程为止.
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：
>当IsGrouping为true时,仅使用ItemContainerGenerator方法,否则继续使用默认的ScrollIntoView.>检查ItemContainerGenerator是否准备就绪,如果是这样调度操作,否则监听ItemContainerGenerator状态以更改..这很重要,就好像它已经准备就绪,然后StatusChanged事件将永远不会触发.