语境
我们有一个内部托管许多视图的 WPF 控件。这些视图又是其他 WPF 控件。视图基于作为主视图一部分的下拉菜单变得可见。父级最终使用ToolkitElementHost. 主视图和两个子视图具有为我们的测试用例定义的自定义自动化对等点。被OnCreateAutomationPeer所有视图覆盖。父视图调用OnCreateAutomationPeer子视图。所有视图都使用DataContext父视图（即由树层次结构组成的 ViewModel）。
问题陈述
主视图是作为 Prism 模块的一部分创建的。但是，DataContext在初始化期间未设置。根据DataContext整个 UI 容器服务的初始化，在稍后的时间点设置。在某些情况下，我们观察到OnCreateAutomationPeer即使snoop在系统上运行了类似的显式 AutomationClient 也会触发。这会导致在调用NullReferenceException中抛出，因为for 子视图仍然为空。OnCreateAutomationPeerDataContext
到目前为止尝试过的解决方案
我们可以通过简单地进行空检查并从中返回空值来克服这个问题OnCreateAutomationPeer。重复调用此方法。在DataContext最终设置了一段时间后，OnCreateAutomationPeer得到了正确的值。一般来说，关于 StackOverflow 的建议是不要禁用 AutomationPeer。
问题
- 在什么时候
DataContext从父控件传递到子控件？ - 是否取决于父视图中设置
DataContext和调用的顺序？InitializeComponent - 我们如何使我们的代码更具确定性，以便我们不必依赖子视图中的 DataContext 的空检查？
- 如何在父视图级别进行测试？这是为了确保未来的更改不会再次破坏此功能。
调用栈
at MyChildView.OnCreateAutomationPeer()
at System.Windows.UIElement.CreateAutomationPeer()
at System.Windows.Automation.Peers.UIElementAutomationPeer.iterate(DependencyObject parent, IteratorCallback callback)
at System.Windows.Automation.Peers.UIElementAutomationPeer.iterate(DependencyObject parent, IteratorCallback callback)
at System.Windows.Automation.Peers.UIElementAutomationPeer.iterate(DependencyObject parent, IteratorCallback callback)
at System.Windows.Automation.Peers.UIElementAutomationPeer.iterate(DependencyObject parent, IteratorCallback callback)
at System.Windows.Automation.Peers.UIElementAutomationPeer.iterate(DependencyObject parent, IteratorCallback callback)
at System.Windows.Automation.Peers.UIElementAutomationPeer.GetChildrenCore()
at MyCustomControl.AutomationProvider.CustomAutomationPeer.GetChildrenCore()
at System.Windows.Automation.Peers.AutomationPeer.EnsureChildren()
at System.Windows.Automation.Peers.AutomationPeer.GetChildren()
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.isDescendantOf(AutomationPeer parent)
at System.Windows.Automation.Peers.AutomationPeer.ValidateConnected(AutomationPeer connectedPeer)
at MS.Internal.Automation.ElementProxy.StaticWrap(AutomationPeer peer, AutomationPeer referencePeer)
at System.Windows.Automation.Peers.AutomationPeer.RaiseAutomationEvent(AutomationEvents eventId)
at System.Windows.Automation.Peers.SelectorAutomationPeer.RaiseSelectionEvents(SelectionChangedEventArgs e)
at System.Windows.Controls.TabControl.OnSelectionChanged(SelectionChangedEventArgs e)
at System.Windows.Controls.Primitives.Selector.SelectionChanger.End()
at System.Windows.Controls.Primitives.Selector.SelectionChanger.SelectJustThisItem(ItemInfo info, Boolean assumeInItemsCollection)
at System.Windows.Controls.Primitives.Selector.OnSelectedIndexChanged(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.StyleHelper.ApplyTemplatedParentValue(DependencyObject container, FrameworkObject child, Int32 childIndex, FrugalStructList`1& childRecordFromChildIndex, DependencyProperty dp, FrameworkElementFactory templateRoot)
at System.Windows.StyleHelper.InvalidatePropertiesOnTemplateNode(DependencyObject container, FrameworkObject child, Int32 childIndex, FrugalStructList`1& childRecordFromChildIndex, Boolean isDetach, FrameworkElementFactory templateRoot)
at System.Windows.FrameworkTemplate.InvalidatePropertiesOnTemplate(DependencyObject container, Object currentObject)
at System.Windows.FrameworkTemplate.HandleBeforeProperties(Object createdObject, DependencyObject& rootObject, DependencyObject container, FrameworkElement feContainer, INameScope nameScope)
at System.Windows.FrameworkTemplate.<>c__DisplayClass45_0.<LoadOptimizedTemplateContent>b__2(Object sender, XamlObjectEventArgs args)
at System.Xaml.XamlObjectWriter.OnBeforeProperties(Object value)
at System.Xaml.XamlObjectWriter.Logic_CreateAndAssignToParentStart(ObjectWriterContext ctx)
at System.Xaml.XamlObjectWriter.WriteStartMember(XamlMember property)
at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlReader templateReader, XamlObjectWriter currentWriter)
at System.Windows.FrameworkTemplate.LoadTemplateXaml(XamlObjectWriter objectWriter)
at System.Windows.FrameworkTemplate.LoadOptimizedTemplateContent(DependencyObject container, IComponentConnector componentConnector, IStyleConnector styleConnector, List`1 affectedChildren, UncommonField`1 templatedNonFeChildrenField)
at System.Windows.FrameworkTemplate.LoadContent(DependencyObject container, List`1 affectedChildren)
at System.Windows.StyleHelper.ApplyTemplateContent(UncommonField`1 dataField, DependencyObject container, FrameworkElementFactory templateRoot, Int32 lastChildIndex, HybridDictionary childIndexFromChildID, FrameworkTemplate frameworkTemplate)
at System.Windows.FrameworkTemplate.ApplyTemplateContent(UncommonField`1 templateDataField, FrameworkElement container)
at System.Windows.FrameworkElement.ApplyTemplate()
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, Boolean& hasDesiredSizeUChanged)
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.Grid.MeasureCell(Int32 cell, Boolean forceInfinityV)
at System.Windows.Controls.Grid.MeasureCellsGroup(Int32 cellsHead, Size referenceSize, Boolean ignoreDesiredSizeU, Boolean forceInfinityV, Boolean& hasDesiredSizeUChanged)
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.DockPanel.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.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.SetLayoutSize()
at System.Windows.Interop.HwndSource.set_RootVisualInternal(Visual value)
at System.Windows.Forms.Integration.ElementHost.<OnHandleCreated>b__54_0()
at System.Windows.Threading.Dispatcher.Invoke(Action callback, DispatcherPriority priority, CancellationToken cancellationToken, TimeSpan timeout)
at System.Windows.Threading.Dispatcher.Invoke(Action callback)
at System.Windows.Forms.Integration.ElementHost.OnHandleCreated(EventArgs e)
at System.Windows.Forms.Control.WmCreate(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.Integration.ElementHost.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr