如何在PresentationFramework中调试NullReferenceException？

Question

我的.NET 4应用程序使用WPF TreeView，我已经增强了它以启用键盘导航和延迟加载。我的问题是，很少会抛出下面显示的异常。在我开发的几个月里，这只发生过一次，我收到了一些客户的错误报告，这些客户偶尔会得到这个。很少见，我无法改变一些东西，玩一下应用程序一段时间，并知道问题是否已经消失。

但是我的主要问题是：堆栈跟踪只显示Microsoft代码，那里没有任何内容。这是.NET / WPF中的错误吗？是否有任何机会找到根本原因？

Type: System.NullReferenceException
Message: Object reference not set to an instance of an object.
Source: PresentationFramework
Stack trace:    at System.Windows.Controls.ItemContainerGenerator.ContainerFromIndex(Int32 index)
  at System.Windows.Controls.TreeViewItem.FindNextFocusableItem(Boolean walkIntoSubtree)
  at System.Windows.Controls.TreeViewItem.InternalPredictFocus(FocusNavigationDirection direction)
  at System.Windows.Controls.VirtualizingStackPanel.FocusChanged(KeyboardFocusChangedEventArgs e)
  at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
  at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
  at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
  at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
  at System.Windows.Input.InputManager.ProcessStagingArea()
  at System.Windows.Input.KeyboardDevice.ChangeFocus(DependencyObject focus, Int32 timestamp)
  at System.Windows.Input.KeyboardDevice.Focus(DependencyObject focus, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
  at System.Windows.Input.KeyboardDevice.Focus(IInputElement element)
  at System.Windows.UIElement.Focus()
  at System.Windows.Controls.TreeViewItem.OnItemsChanged(NotifyCollectionChangedEventArgs e)
  at System.Windows.Controls.ItemsControl.OnItemCollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
  at System.Collections.Specialized.NotifyCollectionChangedEventHandler.Invoke(Object sender, NotifyCollectionChangedEventArgs e)
  at System.Windows.Data.CollectionView.OnCollectionChanged(NotifyCollectionChangedEventArgs args)
  at System.Windows.Controls.ItemCollection.SetCollectionView(CollectionView view)
  at System.Windows.Controls.ItemsControl.OnItemsSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
  at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
  at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
  at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
  at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
  at System.Windows.Data.BindingExpressionBase.Invalidate(Boolean isASubPropertyChange)
  at System.Windows.Data.BindingExpression.Activate(Object item)
  at System.Windows.Data.BindingExpression.OnDataContextChanged(DependencyObject contextElement)
  at System.Windows.Data.BindingExpression.HandlePropertyInvalidation(DependencyObject d, DependencyPropertyChangedEventArgs args)
  at System.Windows.Data.BindingExpressionBase.OnPropertyInvalidation(DependencyObject d, DependencyPropertyChangedEventArgs args)
  at System.Windows.Data.BindingExpression.OnPropertyInvalidation(DependencyObject d, DependencyPropertyChangedEventArgs args)
  at System.Windows.DependentList.InvalidateDependents(DependencyObject source, DependencyPropertyChangedEventArgs sourceArgs)
  at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
  at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
  at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
  at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
  at System.Windows.Controls.ItemContainerGenerator.System.Windows.Controls.Primitives.IItemContainerGenerator.RemoveAll()
  at System.Windows.Controls.VirtualizingStackPanel.ClearAllContainers(ItemsControl itemsControl)
  at System.Windows.Controls.ItemsControl.MS.Internal.Controls.IGeneratorHost.ClearContainerForItem(DependencyObject container, Object item)
  at System.Windows.Controls.ItemContainerGenerator.UnlinkContainerFromItem(DependencyObject container, Object item)
  at System.Windows.Controls.ItemContainerGenerator.Remove(GeneratorPosition position, Int32 count, Boolean isRecycling)
  at System.Windows.Controls.VirtualizingStackPanel.CleanupRange(IList children, IItemContainerGenerator generator, Int32 startIndex, Int32 count)
  at System.Windows.Controls.VirtualizingStackPanel.CleanupContainers(Int32 firstViewport, ItemsControl itemsControl)
  at System.Windows.Controls.VirtualizingStackPanel.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
  at System.Windows.Controls.ItemsPresenter.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.TreeViewItem.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.VirtualizingStackPanel.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
  at System.Windows.Controls.ItemsPresenter.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.TreeViewItem.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.VirtualizingStackPanel.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
  at System.Windows.Controls.ItemsPresenter.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.TreeViewItem.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.VirtualizingStackPanel.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
  at System.Windows.Controls.ItemsPresenter.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.TreeViewItem.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.VirtualizingStackPanel.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
  at System.Windows.Controls.ItemsPresenter.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.TreeViewItem.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.VirtualizingStackPanel.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
  at System.Windows.Controls.ItemsPresenter.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
  at System.Windows.Controls.ScrollContentPresenter.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.ScrollViewer.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Border.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Control.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV)
  at System.Windows.Controls.Grid.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at MS.Internal.Helper.MeasureElementWithSingleChild(UIElement element, Size constraint)
  at System.Windows.Controls.ContentPresenter.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Border.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.Controls.Control.MeasureOverride(Size constraint)
  at System.Windows.FrameworkElement.MeasureCore(Size availableSize)
  at System.Windows.UIElement.Measure(Size availableSize)
  at System.Windows.ContextLayoutManager.UpdateLayout()
  at System.Windows.Interop.HwndSource.Process_WM_SIZE(UIElement rootUIElement, IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam)
  at System.Windows.Interop.HwndSource.LayoutFilterMessage(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)
Target: System.Windows.DependencyObject ContainerFromIndex(Int32)
Inner exception message:

注意：我的机器上也有这个，它运行完全修补的Windows 7 x64。

Answer 1

我个人从未发现过WPF中的错误。但是，进入WPF代码经常使我能够将问题的根源追溯到自己。

以下是一些有关如何启用调试框架源的MSDN文章：

• Visual Studio 2008 version
• Visual Studio 2010 version

指向所有版本的链接：https://msdn.microsoft.com/en-us/library/cc667410.aspx