That would be very hard to accomplish, I'm afraid. So far I've only seen this issue once. And I cannot reproduce it with the full application either.

Given that you have the call stack, you may want to consider catching the exception at this location.

Do as you wish - this was more a notification that you may have an issue here when there are multiple UI threads in play.

We are currently locked to version 13.1.20131.2204.  What is the latest hotfix version for 13.1?

I was able to test with the 2336 version and the issue still happens every time.  Still unable to reproduce in a test app even while using the same OCX control in the pane.  Attached is the video showing the flow and how the exception is happening.  Note the undocked window is not closed or closing when the exception occurs.  It still seems like a timing with this call that assumes it would be visible.  If it was closing or closed wouldn't the undocked window go away?

I'm wondering if changing 

IntPtr handle = new WindowInteropHelper((Window) this).Handle;

to

IntPtr handle = new WindowInteropHelper((Window) this).EnsureHandler();

would fix this issue for us.  The value of this._isClosing = false at the time of the error so I'm still pretty sure it isn't closing.  Seems like the native window isn't ready yet.

In ToolWindowHostWindow.cs

protected override void OnSourceInitialized(EventArgs e)
{
this.SetFlag(ToolWindowHostWindow.InternalFlags.HasSourceBeenInitialized, true);
IntPtr handle = new WindowInteropHelper((Window) this).Handle;
HwndSource.FromHwnd(handle).AddHook(new HwndSourceHook(this.WndProc));
PresentationSource.AddSourceChangedHandler((IInputElement) this, new SourceChangedEventHandler(this.OnPresentationSourceChanged));
if (this._content != null)
{
this.SetBinding(ToolWindowHostWindow.WindowStateInternalProperty, (BindingBase) Utilities.CreateBindingObject(ToolWindow.WindowStateProperty, BindingMode.TwoWay, (object) this._content));
if (this._content != null && this.WindowState != WindowState.Normal)
{
Rect restoreBounds = this._content.GetRestoreBounds(false);
if (NativeWindowMethods.GetWindowState((Window) this) == WindowState.Normal && this.WindowState == WindowState.Minimized && !restoreBounds.IsEmpty)
this.Dispatcher.BeginInvoke(DispatcherPriority.Normal, (Delegate) new SendOrPostCallback(this.AsyncInitializeRestoreBounds), (object) restoreBounds);
else
this.SetRestoreBounds(handle, restoreBounds);
}
this.UseSystemNonClientArea = this.UseSystemNonClientArea;
}
this.VerifyWindowStyleBits(handle);
ToolWindowHostWindow.UpdateAllowClose((Window) this, this.AllowClose);
this.VerifyRelativePositionBinding();
this.SynchronizeLocation(true);
base.OnSourceInitialized(e);
this.VerifyIsInView(false, true, false);
}

Hmmm... I do see the this.IsDisposed == true.  So you are right it is getting closed somehow.  The this.Title was set to an empty string so I'm not sure if the window I undocked was the same window that is causing this exception.

Great. I'm glad you were able to get around the issue and hopefully the debugging snippets could help someone else in the future who might encounter this issue (with an older version anyway as we'll make a change to avoid the re-entrant MouseMove message processing during the drag).

Thank you for all your help and the workaround.  I wasn't able to get the Capture Mouse workaround to work but BeginInvoke the FitWidth at Application Idle priority seems to be enough to prevent the issue.  At this point I consider the issue closed.

Thanks for the input and your patience on this one.

So basically what seems to be happening is that while we are processing the MouseMove we are trying to show the tool window. As part of showing a Window WPF will call UpdateLayout. You have code in your ItemViewerUC that is listening to the SizeChanged and you are calling FitWidth on the OCX. When trying to communicate with the OCX the framework is processing the queued messages which at least in this case includes another MouseMove which results in a re-entrancy (i.e. they invoke the MouseMove while they are already in the middle of processing a MouseMove).

Since we close/remove a toolwindow that doesn't contain any visible panes this causes us to call Close on the toolwindow which in this case is in the middle of a show (from the 1st MouseMove that is still in progress). So one option is for you to asynchronously process the SizeChanged (or perhaps skip it entirely if the window is in the middle of a show). Another might be to try and capture the MouseMove while you are calling FitWidth.

e.g.

var fe = Mouse.Captured as FrameworkElement;
 MouseEventHandler mouseHandler = (obj, args) =>
 {
 args.Handled = true;
 };
if (fe != null)
 fe.AddHandler(PreviewMouseMoveEvent, mouseHandler);
// do your OCX changes
if (fe != null)
 fe.RemoveHandler(PreviewMouseMoveEvent, mouseHandler);

We can add code to ignore a mousemove while we are processing one during a drag but you'll need to do one of the above workarounds or something else since you won't be able to upgrade to 13.2 or later.

This is the last stack trace I got with the provided debug code before the thrown exception.

at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo)
at System.Environment.get_StackTrace()
at ToolWindowDebugger.DebugHelper.OnToolWindowClosing(Object sender, CancelEventArgs e) in c:\_DevEnvs\Syn 32bit Crt\Synergy Client\UI\App.xaml.cs:line 351
at System.Windows.Window.OnClosing(CancelEventArgs e)
at Infragistics.Windows.Controls.ToolWindowHostWindow.OnClosing(CancelEventArgs e)
at System.Windows.Window.WmClose()
at System.Windows.Window.WindowFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at System.Windows.Interop.HwndSource.PublicHooksFilterMessage(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.UnsafeSendMessage(IntPtr hWnd, WindowMessage msg, IntPtr wParam, IntPtr lParam)
at System.Windows.Window.InternalClose(Boolean shutdown, Boolean ignoreCancel)
at System.Windows.Window.Close()
at Infragistics.Windows.Controls.ToolWindowHostWindow.CloseHelperImpl()
at Infragistics.Windows.Controls.ToolWindowHostWindow.CloseHelper()
at Infragistics.Windows.Controls.ToolWindowHostWindow.Infragistics.Windows.Controls.IToolWindowHost.Close()
at Infragistics.Windows.Controls.ToolWindow.CloseOverride()
at Infragistics.Windows.DockManager.PaneToolWindow.CloseOverride()
at Infragistics.Windows.Controls.ToolWindow.Close()
at Infragistics.Windows.DockManager.PaneToolWindow.OnChildVisibilityChanged(Object sender, RoutedEventArgs e)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
at Infragistics.Windows.DockManager.DockManagerUtilities.RaiseVisibilityChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
at Infragistics.Windows.DockManager.SplitPane.OnVisibilityChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.PropertyChangedCallback.Invoke(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.DependencyObject.CoerceValue(DependencyProperty dp)
at Infragistics.Windows.DockManager.SplitPane.OnChildrenCollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
at System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
at Infragistics.Collections.ObservableCollectionExtended`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
at Infragistics.Windows.DockManager.ObservableSplitElementCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
at Infragistics.Collections.ObservableCollectionExtended`1.RemoveItem(Int32 index)
at System.Collections.ObjectModel.Collection`1.RemoveAt(Int32 index)
at Infragistics.Windows.DockManager.SplitPane.Infragistics.Windows.DockManager.IContentPaneContainer.RemoveContentPane(ContentPane pane, Boolean replaceWithPlaceholder)
at Infragistics.Windows.DockManager.DockManagerUtilities.MovePane(ContentPane pane, IContentPaneContainer newContainer, Nullable`1 newIndex, PaneLocation newLocation, MovePaneHelper moveHelper)
at Infragistics.Windows.DockManager.Dragging.DragManager.CloneRootDragElement(PaneLocation newLocation, Action`1 initializeNewSplit)
at Infragistics.Windows.DockManager.Dragging.DragManager.CreateWindowBeingDragged(Point location, Size size)
at Infragistics.Windows.DockManager.Dragging.FloatPaneAction.PerformAction(DragManager dragManager, Boolean isPreview)
at Infragistics.Windows.DockManager.Dragging.DragManager.ProcessDragMove(IInputDeviceInfo e, Nullable`1 windowRect)
at Infragistics.Windows.DockManager.Dragging.DragManager.ProcessDragMove(MouseEventArgs e)
at Infragistics.Windows.DockManager.Dragging.DragManager.OnDragElementMouseMove(Object sender, MouseEventArgs e)
at System.Windows.Input.MouseEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.ContentElement.RaiseTrustedEvent(RoutedEventArgs args)
at System.Windows.Input.InputManager.ProcessStagingArea()
at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at System.Windows.Interop.HwndSource.InputFilterMessage(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 System.RuntimeType.InvokeDispMethod(String name, BindingFlags invokeAttr, Object target, Object[] args, Boolean[] byrefModifiers, Int32 culture, String[] namedParameters)
at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams)
at System.RuntimeType.ForwardCallToInvokeMember(String memberName, BindingFlags flags, Object target, Int32[] aWrapperTypes, MessageData& msgData)
at SynDocViewerLib._DSynDocViewer.FitWidth(Int32 lFit)
at AxSynDocViewerLib.AxSynDocViewer.FitWidth(Int32 lFit)
at SynDocViewerWrapper.SynDocViewerWrap.FitWidth(Boolean bFit) in c:\_DevEnvs\Syn 32bit Crt\Synergy Capture\SynDocViewerWrapper\SynDocViewerWrap.cs:line 1302
at SynergyECM.Controls.ItemViewerUC.fitWidthAndTextWidth() in c:\_DevEnvs\Syn 32bit Crt\Synergy Controls\SynViewerCntrls\ItemViewerUC\ItemViewerUC.xaml.cs:line 4131
at SynergyECM.Controls.ItemViewerUC.docViewerHostGrid_SizeChanged(Object sender, SizeChangedEventArgs e) in c:\_DevEnvs\Syn 32bit Crt\Synergy Controls\SynViewerCntrls\ItemViewerUC\ItemViewerUC.xaml.cs:line 1787
at System.Windows.SizeChangedEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
at System.Windows.FrameworkElement.OnRenderSizeChanged(SizeChangedInfo sizeInfo)
at System.Windows.ContextLayoutManager.fireSizeChangedEvents()
at System.Windows.ContextLayoutManager.UpdateLayout()
at System.Windows.UIElement.UpdateLayout()
at System.Windows.Interop.HwndSource.SetLayoutSize()
at System.Windows.Interop.HwndSource.set_RootVisualInternal(Visual value)
at System.Windows.Interop.HwndSource.set_RootVisual(Visual value)
at System.Windows.Window.SetRootVisual()
at System.Windows.Window.SetRootVisualAndUpdateSTC()
at System.Windows.Window.SetupInitialState(Double requestedTop, Double requestedLeft, Double requestedWidth, Double requestedHeight)
at System.Windows.Window.CreateSourceWindow(Boolean duringShow)
at System.Windows.Window.CreateSourceWindowDuringShow()
at System.Windows.Window.SafeCreateWindowDuringShow()
at System.Windows.Window.ShowHelper(Object booleanBox)
at System.Windows.Window.Show()
at Infragistics.Windows.Controls.ToolWindowHostWindow.Show(Boolean activate)
at Infragistics.Windows.Controls.ToolWindowHostWindow.DeferShowHelper.Show(Boolean activate)
at Infragistics.Windows.Controls.ToolWindow.DeferredShowInfo.ProcessShow(Boolean cancel)
at Infragistics.Windows.Controls.ToolWindow.DeferredShowInfo.System.IDisposable.Dispose()
at Infragistics.Windows.DockManager.PaneToolWindow.ResumeSyncShow()
at Infragistics.Windows.DockManager.MovePaneHelper.OnToolWindowChanged(PaneToolWindow oldWindow, PaneToolWindow newWindow)
at Infragistics.Windows.DockManager.MovePaneHelper.OnToolWindowChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
at System.Windows.DependencyObject.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.DependencyObject.ClearValueCommon(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata)
at System.Windows.DependencyObject.ClearValue(DependencyProperty dp)
at System.Windows.Data.BindingOperations.ClearBinding(DependencyObject target, DependencyProperty dp)
at Infragistics.Windows.DockManager.MovePaneHelper.System.IDisposable.Dispose()
at Infragistics.Windows.DockManager.Dragging.DragManager.CloneRootDragElement(PaneLocation newLocation, Action`1 initializeNewSplit)
at Infragistics.Windows.DockManager.Dragging.DragManager.CreateWindowBeingDragged(Point location, Size size)
at Infragistics.Windows.DockManager.Dragging.FloatPaneAction.PerformAction(DragManager dragManager, Boolean isPreview)
at Infragistics.Windows.DockManager.Dragging.DragManager.ProcessDragMove(IInputDeviceInfo e, Nullable`1 windowRect)
at Infragistics.Windows.DockManager.Dragging.DragManager.ProcessDragMove(MouseEventArgs e)
at Infragistics.Windows.DockManager.Dragging.DragManager.OnDragElementMouseMove(Object sender, MouseEventArgs e)
at System.Windows.Input.MouseEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.ContentElement.RaiseTrustedEvent(RoutedEventArgs args)
at System.Windows.Input.InputManager.ProcessStagingArea()
at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at System.Windows.Interop.HwndSource.InputFilterMessage(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 SynergyECM.Client.UI.SynergyClientApp.Main() in c:\_DevEnvs\Syn 32bit Crt\Synergy Client\UI\obj\x86\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()

I'll give it try and yes, at this point I haven't been able to isolate the cause into a test application.