我遇到了一些奇怪的行为，似乎无法解决。当我迭代我的ListBox.ItemsSource属性中的项目时，我无法获取容器？我期望看到返回一个ListBoxItem，但只得到null。
有什么想法吗？
这是我使用的代码：
this.lstResults.ItemsSource.ForEach(t =>
{
ListBoxItem lbi = this.lstResults.ItemContainerGenerator.ContainerFromItem(t) as ListBoxItem;
if (lbi != null)
{
this.AddToolTip(lbi);
}
});
ItemsSource目前设置为字典，并包含许多键值对。
我在StackOverflow上找到了一个对我的情况更有效的解决方案：
在调用ContainerFromItem或ContainerFromIndex之前，通过添加UpdateLayout和ScrollIntoView调用，可以使DataGrid的那一部分得以实现，这使得它能够为ContainerFromItem/ContainerFromIndex返回一个值：
dataGrid.UpdateLayout();
dataGrid.ScrollIntoView(dataGrid.Items[index]);
var row = (DataGridRow)dataGrid.ItemContainerGenerator.ContainerFromIndex(index);
如果你不想让DataGrid中当前位置改变，那么这可能不是一个好的解决方案，但如果可以接受，它可以在不关闭虚拟化的情况下工作。
最终解决了问题... 通过在我的XAML中添加VirtualizingStackPanel.IsVirtualizing="False"，现在一切都像预期的那样工作。
不过，我错过了虚拟化的所有性能优势，所以我将我的加载路由更改为异步，并在我的列表框中添加了一个“旋转器”来进行加载...
object viewItem = list.ItemContainerGenerator.ContainerFromItem(item);
if (viewItem == null)
{
list.UpdateLayout();
viewItem = list.ItemContainerGenerator.ContainerFromItem(item);
Debug.Assert(viewItem != null, "list.ItemContainerGenerator.ContainerFromItem(item) is null, even after UpdateLayout");
}
item和list的变量，而没有说明它们是什么。 - Stealth Rabbias转换只是错误的，因此将其转换为null（您可以使用普通转换来获取正确的异常）。ItemsControl为大多数项目进行虚拟化时，任何时候都不会存在容器。ItemsControl.ItemContainerStyle）。使用此订阅：
TheListBox.ItemContainerGenerator.StatusChanged += (sender, e) =>
{
TheListBox.Dispatcher.Invoke(() =>
{
var TheOne = TheListBox.ItemContainerGenerator.ContainerFromIndex(0);
if (TheOne != null)
// Use The One
});
};
IsExpanded和IsSelected添加到基础对象中，并在TreeViewItem样式中绑定它们，虽然在某些情况下这个方法大多数情况下可行，但仍然会失败...注意：我的目标是编写一个迷你/自定义资源管理器视图，在右侧窗格中单击文件夹时，它会在TreeView上被选中，就像在资源管理器中一样。private void ListViewItem_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
var item = sender as ListViewItem;
var node = item?.Content as DirectoryNode;
if (node == null) return;
var nodes = (IEnumerable<DirectoryNode>)TreeView.ItemsSource;
if (nodes == null) return;
var queue = new Stack<Node>();
queue.Push(node);
var parent = node.Parent;
while (parent != null)
{
queue.Push(parent);
parent = parent.Parent;
}
var generator = TreeView.ItemContainerGenerator;
while (queue.Count > 0)
{
var dequeue = queue.Pop();
TreeView.UpdateLayout();
var treeViewItem = (TreeViewItem)generator.ContainerFromItem(dequeue);
if (queue.Count > 0) treeViewItem.IsExpanded = true;
else treeViewItem.IsSelected = true;
generator = treeViewItem.ItemContainerGenerator;
}
}
在这里使用了多个技巧：
null到目前为止，它运行得非常好，
ListBoxItem容器（请参阅https://msdn.microsoft.com/en-us/library/system.windows.controls.virtualizingstackpanel(v=vs.110).aspx#Anchor_9）。ListBox，我建议改用ListView - 它继承自ListBox并支持ScrollIntoView()方法，您可以利用该方法来控制虚拟化；targetListView.ScrollIntoView(itemVM);
DoEvents();
ListViewItem itemContainer = targetListView.ItemContainerGenerator.ContainerFromItem(itemVM) as ListViewItem;
上面的示例还使用了在此处更详细解释的DoEvents()静态方法; WPF如何等待绑定更新发生后再处理更多代码?
ListBox和ListView控件之间还有一些其他细微差别(ListBox和ListView之间的区别是什么)，但这不应该对您的使用情况产生实质影响。
ContainerFromItem的.cs文件中禁用它。 VirtualizingStackPanel.SetIsVirtualizing(listBox, false);
这样做可以减少XAML和代码之间的耦合度，从而避免因触碰XAML而破坏代码的风险。
DataGrid。当我在 XAML 中设置 IsVirtualising(false) 时，性能会急剧下降，而当我在 GUI 完全显示后才这样做时，似乎已经太晚了。 - Dominique将VirtualizingStackPanel.IsVirtualizing="False"设置为“True”可以避免控件模糊。请参见下面的实现方法，这有助于我避免同样的问题。
始终将应用程序的VirtualizingStackPanel.IsVirtualizing设置为“True”。详细信息请参见链接。
/// <summary>
/// Recursively search for an item in this subtree.
/// </summary>
/// <param name="container">
/// The parent ItemsControl. This can be a TreeView or a TreeViewItem.
/// </param>
/// <param name="item">
/// The item to search for.
/// </param>
/// <returns>
/// The TreeViewItem that contains the specified item.
/// </returns>
private TreeViewItem GetTreeViewItem(ItemsControl container, object item)
{
if (container != null)
{
if (container.DataContext == item)
{
return container as TreeViewItem;
}
// Expand the current container
if (container is TreeViewItem && !((TreeViewItem)container).IsExpanded)
{
container.SetValue(TreeViewItem.IsExpandedProperty, true);
}
// Try to generate the ItemsPresenter and the ItemsPanel.
// by calling ApplyTemplate. Note that in the
// virtualizing case even if the item is marked
// expanded we still need to do this step in order to
// regenerate the visuals because they may have been virtualized away.
container.ApplyTemplate();
ItemsPresenter itemsPresenter =
(ItemsPresenter)container.Template.FindName("ItemsHost", container);
if (itemsPresenter != null)
{
itemsPresenter.ApplyTemplate();
}
else
{
// The Tree template has not named the ItemsPresenter,
// so walk the descendents and find the child.
itemsPresenter = FindVisualChild<ItemsPresenter>(container);
if (itemsPresenter == null)
{
container.UpdateLayout();
itemsPresenter = FindVisualChild<ItemsPresenter>(container);
}
}
Panel itemsHostPanel = (Panel)VisualTreeHelper.GetChild(itemsPresenter, 0);
// Ensure that the generator for this panel has been created.
UIElementCollection children = itemsHostPanel.Children;
MyVirtualizingStackPanel virtualizingPanel =
itemsHostPanel as MyVirtualizingStackPanel;
for (int i = 0, count = container.Items.Count; i < count; i++)
{
TreeViewItem subContainer;
if (virtualizingPanel != null)
{
// Bring the item into view so
// that the container will be generated.
virtualizingPanel.BringIntoView(i);
subContainer =
(TreeViewItem)container.ItemContainerGenerator.
ContainerFromIndex(i);
}
else
{
subContainer =
(TreeViewItem)container.ItemContainerGenerator.
ContainerFromIndex(i);
// Bring the item into view to maintain the
// same behavior as with a virtualizing panel.
subContainer.BringIntoView();
}
if (subContainer != null)
{
// Search the next level for the object.
TreeViewItem resultContainer = GetTreeViewItem(subContainer, item);
if (resultContainer != null)
{
return resultContainer;
}
else
{
// The object is not under this TreeViewItem
// so collapse it.
subContainer.IsExpanded = false;
}
}
}
}
return null;
}
如果你仍然遇到这个问题，我通过忽略第一个选择更改事件并使用线程来重复调用来解决了这个问题。这是我最终做的：
private int _hackyfix = 0;
private void OnMediaSelectionChanged(object sender, SelectionChangedEventArgs e)
{
//HACKYFIX:Hacky workaround for an api issue
//Microsoft's api for getting item controls for the flipview item fail on the very first media selection change for some reason. Basically we ignore the
//first media selection changed event but spawn a thread to redo the ignored selection changed, hopefully allowing time for whatever is going on
//with the api to get things sorted out so we can call the "ContainerFromItem" function and actually get the control we need I ignore the event twice just in case but I think you can get away with ignoring only the first one.
if (_hackyfix == 0 || _hackyfix == 1)
{
_hackyfix++;
Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
OnMediaSelectionChanged(sender, e);
});
}
//END OF HACKY FIX//Actual code you need to run goes here}
编辑于2014年10月29日：实际上，您甚至不需要线程调度程序代码。您可以将所需内容设置为 null 以触发第一个选择更改事件，然后退出该事件，以便未来的事件按预期工作。
private int _hackyfix = 0;
private void OnMediaSelectionChanged(object sender, SelectionChangedEventArgs e)
{
//HACKYFIX: Daniel note: Very hacky workaround for an api issue
//Microsoft's api for getting item controls for the flipview item fail on the very first media selection change for some reason. Basically we ignore the
//first media selection changed event but spawn a thread to redo the ignored selection changed, hopefully allowing time for whatever is going on
//with the api to get things sorted out so we can call the "ContainerFromItem" function and actually get the control we need
if (_hackyfix == 0)
{
_hackyfix++;
/*
Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
OnMediaSelectionChanged(sender, e);
});*/
return;
}
//END OF HACKY FIX
//Your selection_changed code here
}