在虚拟化的WPF的TreeView滚动很不稳定(Scrolling in virtualized W

如果虚拟化是启用TreeView具有各种尺寸的商品，多次出现的问题：

垂直滚动条随机改变它的大小和查看整个树后不记得了元件的尺寸。用鼠标滚动难。
一些向上和向下滚动后， ArgumentNullException从框架代码抛出。

Reproduciing很简单：创建一个新的WPF应用程序，然后把该代码放到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>

这段代码添加到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; }
    }
}

当应用程序正在运行，移动鼠标光标成树状，使用鼠标滚轮滚动到底部，然后滚动到顶部，然后重新开始向下滚动。中间的某个位置下面的异常被抛出：

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()

你也可以看到，例外是不是唯一的问题。当上下滚动，滚动条，不断改变其大小。（同样的问题不会出现在ListBox ，其不能预测的大小，但观看整个列表之后记住总高度。）

问：如何使滚动条举止得体，摆脱了异常？（我不介意指向替代的TreeView控件或者支持此方案也许虚拟化面板。）

Answer 1:

为了使链接更加突出，我在回答中张贴了。它看起来像一个bug是框架代码内，并没有还没有找到解决办法。我报告了Microsoft Connect上的错误：

微软连接：在虚拟化的WPF的TreeView滚动很不稳定

还有这是张贴在由@sixlettervariables评论一个可能相关的bug：

微软连接：WPF应用程序冻结，同时滚动特定条件下的TreeView

如果你能重现错误，请投起来。

Answer 2:

默认情况下，虚拟化堆栈面板是采用像素渲染来渲染子元素和循环模式，将丢弃不再需要在UI树视图容器内的每个元素。这会导致滚动条大小来自动改变。该VirtualizationPanel像素渲染技术将导致也减慢滚动选项。通过更改为VirtualizingPanel.ScrollUnit =“项目”，将解决你的问题。下面XAML工作对我罚款

<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 3:

我已经在WPF应用程序采取同样的错误，同时加载窗口。的Visual Studio 2017年一些经过研究发现了这样的事情后，我已经注意到有趣的是WindowStyle元素。

在我的情况在WPF和XAML的窗户设计窗口中的错误属性值