WPF OnCreateAutomationPeer Invoked Too Early Before DataContext is Set

Question

Context

We have a WPF control which internally hosts many views. These views are in turn other WPF controls. The views become visible based on a drop-drop which is part of the main view. The parent is finally run inside a legacy Windows Forms application using ToolkitElementHost. The main view and two sub views have custom automation peers defined for our test cases. The OnCreateAutomationPeer is overridden in all the views. The parent view calls the OnCreateAutomationPeer on the child views. All the views use the DataContext of parent view (which is ViewModel consisting of tree hierarchy).

Problem Statement

The main view is created using as part of a Prism module. However, the DataContext is not set during initialization. The DataContext is set at a later point of time as per initialization of whole UI container service. In certain cases we are observing that the OnCreateAutomationPeer is triggered even though there is explicit AutomationClient like snoop running on the system. This causes NullReferenceException thrown in the OnCreateAutomationPeer call because the DataContext for child view is still null.

Solution Tried So Far

We can overcome this by simply putting a null check and returning null value from OnCreateAutomationPeer. There are repeated calls to this method. After some time when the DataContext is finally set, the OnCreateAutomationPeer gets the correct values. In general the advice on StackOverflow is not to disable AutomationPeer.

Questions

1. At what point of time the DataContext is passed on to the child control from parent control?
2. Does it depend on the order of setting DataContext and calling InitializeComponent in the parent view?
3. How can we make our code more deterministic so that we do not have to rely on null checks for DataContext in the child views?
4. How can this be tested at the level of parent view? This is to make sure the future changes do not break this functionality again.

CallStack

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