Question

如果在TreeView中启用了具有各种尺寸的项目的虚拟化，则会出现多个问题：

垂直滚动条随机更改其大小，并且在查看整个树后不记得元素的大小。用鼠标滚动很难。
在向上和向下滚动之后，框架代码中会抛出ArgumentNullException。

重现很简单：创建一个新的WPF应用程序，然后将此代码放入 MainWindow.xaml

<Window x:Class="VirtualTreeView.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="800" Width="400" Left="0" Top="0"
        DataContext="{Binding RelativeSource={RelativeSource Self}}">
    <Grid>
        <TreeView x:Name="tvwItems" ItemsSource="{Binding Items}"
                VirtualizingPanel.IsVirtualizing="True" VirtualizingPanel.VirtualizationMode="Recycling">
            <TreeView.ItemTemplate>
                <DataTemplate>
                    <Border Height="{Binding Height}" Width="{Binding Height}"
                            BorderThickness="1" Background="DarkGray" BorderBrush="DarkBlue"/>
                </DataTemplate>
            </TreeView.ItemTemplate>
        </TreeView>
    </Grid>
</Window>

将此代码转换为 MainWindow.xaml.cs

using System.Collections.ObjectModel;
using System.Linq;

namespace VirtualTreeView
{
    public partial class MainWindow
    {
        public ObservableCollection<Item> Items { get; set; }

        public MainWindow ()
        {
            Items = new ObservableCollection<Item>(Enumerable.Range(0, 20).Select(i => new Item {
                Height = i*20,
            }));
            InitializeComponent();
        }
    }

    public class Item
    {
        public double Height { get; set; }
    }
}

运行应用程序时，将鼠标光标移动到树视图中，使用鼠标滚轮滚动到底部，然后滚动到顶部，然后再次向下滚动。在中间某处抛出以下异常：

System.ArgumentNullException was unhandled
  HResult=-2147467261
  Message=Value cannot be null.
Parameter name: element
  Source=PresentationCore
  ParamName=element
  StackTrace:
       at MS.Internal.Media.VisualTreeUtils.AsNonNullVisual(DependencyObject element, Visual& visual, Visual3D& visual3D)
       at System.Windows.Media.VisualTreeHelper.GetParent(DependencyObject reference)
       at System.Windows.Controls.VirtualizingStackPanel.FindScrollOffset(Visual v)
       at System.Windows.Controls.VirtualizingStackPanel.OnAnchorOperation(Boolean isAnchorOperationPending)
       at System.Windows.Controls.VirtualizingStackPanel.OnAnchorOperation()
       at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
       at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
       at System.Windows.Threading.DispatcherOperation.InvokeImpl()
       at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Windows.Threading.DispatcherOperation.Invoke()
       at System.Windows.Threading.Dispatcher.ProcessQueue()
       at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
       at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
       at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
       at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
       at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
       at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
       at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
       at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
       at System.Windows.Threading.Dispatcher.Run()
       at System.Windows.Application.RunDispatcher(Object ignore)
       at System.Windows.Application.RunInternal(Window window)
       at System.Windows.Application.Run(Window window)
       at System.Windows.Application.Run()
       at VirtualTreeView.App.Main() in d:\Docs\Projects\_Try\VirtualTreeView\obj\Debug\App.g.cs:line 0
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()

您还可以看到异常不是唯一的问题。向上和向下滚动时，滚动条会不断更改其大小。（同样的问题不会出现在ListBox中，它无法预测大小，但会在查看整个列表后记住总高度。）

问题：如何使滚动条正常运行并摆脱异常？（我不介意链接到替代TreeView控件或可能支持此场景的虚拟化面板。）

Answer 1

为了使链接更加突出，我也将其发布在答案中。它看起来像是框架代码中的错误，并且还没有找到变通方法。我已经报告了Microsoft Connect上的错误：

Microsoft Connect: Scrolling in virtualized WPF TreeView is very unstable

@sixlettervariables在评论中也发布了一个可能相关的错误：

Microsoft Connect: WPF application freezes while scrolling the TreeView under specific conditions

如果您可以重现错误，请将其投票。

Answer 2

从 .NET 5 开始，这个问题仍然存在于 WPF 中，而且微软已经停用了 Microsoft Connect，因此不清楚这是否已经在他们的关注范围内。我遇到了同样的问题，并偶然发现了一个对我有用的修复程序。本质上，它只是做 TreeView 应该做的事情，使用 HierarchichalDataTemplate 来呈现每个节点，但是在滚动时内置 TreeView 崩溃的地方，这个版本没有（在我的情况下是在项目树上）。

<DockPanel>
   <DockPanel.Resources>
      <HierarchicalDataTemplate DataType="{x:Type src:Item}" ItemsSource="{Binding Path=Children}">
         <TextBlock Text"{Binding}"/>
      </HierarchicalDataTemplate>
   </DockPanel.Resources>

   <TreeView x:Name="tvwItems" VirtualizingStackPanel.IsVirtualizing="True" VirtualizingStackPanel.VirtualizationMode="Recycling" ItemsSource="{Binding Items}">
   </TreeView>
</DockPanel>

Answer 3

默认情况下，Virtualization Stack面板使用像素渲染来渲染子元素，而Recycling模式将丢弃在UI视图中容器中不再需要的每个元素。这会导致滚动条大小自动更改。 VirtualizationPanel像素渲染技术也会导致滚动选项变慢。通过更改为VirtualizingPanel.ScrollUnit =“Item”将解决您的问题。 xaml下面对我来说工作正常

<Window x:Class="VirtualTreeView.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="800" Width="400" Left="0" Top="0"
    DataContext="{Binding RelativeSource={RelativeSource Self}}">
<Grid>
    <TreeView x:Name="tvwItems"
              ItemsSource="{Binding Items}"
              VirtualizingPanel.IsVirtualizing="True"
              VirtualizingPanel.VirtualizationMode="Recycling"
              VirtualizingPanel.ScrollUnit="Item"
              >
        <TreeView.ItemTemplate>
            <DataTemplate>
                <Border Height="{Binding Height}"
                        Width="{Binding Height}"
                        BorderThickness="1"
                        Background="DarkGray"
                        BorderBrush="DarkBlue" />
            </DataTemplate>
        </TreeView.ItemTemplate>
    </TreeView>
</Grid>
</Window>

Answer 4

我在加载窗口时在wpf应用程序中遇到了相同的错误。 Visual Studio 2017经过一番研究后发现类似这篇文章，我注意到它是有趣的WindowStyle元素。

对于我来说，wpf和Windows属性值在XAML设计窗口中的错误是

WindowStyle =“ none”

我已将其值更改为WindowStyle ="SingleBorderWindow"，并且此错误已消失

在虚拟化WPF TreeView中滚动非常不稳定

4 个答案: