How to debug the visual tree if an "Must disconnect specified child from current parent Visual before attaching to new parent Visual" exception occurs

Question

How do you debug the following Error?

Must disconnect specified child from current parent Visual before attaching to new parent Visual.

I'm sure i understood the meaning of this Exception but in case I have missed something important here is what I think this means:

An object which based on FrameworkElement does already exist somewhere in the visual-tree and I am trying to add it again somewhere else in the tree.

To work around this I have 2 options:

1. remove it from its current position in the visual-tree, or
2. clone it depending on my implementation.

So far so good but why does this Exception not tell me what type of child I need to modify? Because if the object you are trying to use contains multiple children you have to look in each class to may find the object which throws this Exception.

Is there an easy way to find the object? I think the stack trace isn't really helpful.

Here the stack trace:

UnhandledException=System.ArgumentException: Must disconnect specified child from current parent Visual before attaching to new parent Visual.
   at System.Windows.Media.Visual.AddVisualChild(Visual child)
   at MS.Internal.Documents.FlowDocumentView.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.ScrollContentPresenter.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Grid.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Control.ArrangeOverride(Size arrangeBounds)
   at System.Windows.Controls.ScrollViewer.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Border.ArrangeOverride(Size finalSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Grid.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Control.ArrangeOverride(Size arrangeBounds)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.StackPanel.StackArrangeHelper(IStackMeasure arrangeElement, IStackMeasureScrollData scrollData, Size arrangeSize)
   at System.Windows.Controls.StackPanel.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at MS.Internal.Helper.ArrangeElementWithSingleChild(UIElement element, Size arrangeSize)
   at System.Windows.Controls.ContentPresenter.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Border.ArrangeOverride(Size finalSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Control.ArrangeOverride(Size arrangeBounds)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at MS.Internal.Helper.ArrangeElementWithSingleChild(UIElement element, Size arrangeSize)
   at System.Windows.Controls.ContentPresenter.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Border.ArrangeOverride(Size finalSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Control.ArrangeOverride(Size arrangeBounds)
   at System.Windows.Controls.DataGridCell.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   at System.Windows.Controls.Grid.ArrangeOverride(Size arrangeSize)
   at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
   at System.Windows.UIElement.Arrange(Rect finalRect)
   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 System.Windows.Window.ShowDialog()
   at Speiseplandienst.ViewModels.BestellscheinUebersichtListVM.OnEdit() in C:\_\_\_\_\_\_\_\BestellscheinUebersichtListVM.cs:Line 30.
   at Framework.ListVM.Edit() in C:\_\_\_\_\_\_\Controls\ListVM.cs:Line 118.
   at Framework.ListVM.<get_EditCommand>b__8(Object param) in C:\_\_\_\_\_\_\Controls\ListVM.cs:Line 101.
   at Framework.RelayCommand.Execute(Object parameter) in C:\_\_\_\Framework\Tools\RelayCommand.cs:Line 132.
   at MS.Internal.Commands.CommandHelpers.CriticalExecuteCommandSource(ICommandSource commandSource, Boolean userInitiated)
   at System.Windows.Controls.Primitives.ButtonBase.OnClick()
   at System.Windows.Controls.Button.OnClick()
   at System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
   at System.Windows.UIElement.OnMouseLeftButtonUpThunk(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.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.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
   at System.Windows.UIElement.OnMouseUpThunk(Object sender, MouseButtonEventArgs e)
   at System.Windows.Input.MouseButtonEventArgs.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.RaiseTrustedEvent(RoutedEventArgs args)
   at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
   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 Speiseplandienst.MainRun.Main(String[] args) in C:\_\_\_\_\_\_\Main.cs:Line 18.

Answer 1

This error can have many different causes. For example, if you try to add the same Visual object into a UI collection control more than once, this error will occur. If you try to add the selected items (UI objects) from one ListBox to another (rather than just adding the data), you will get this error. If you try to set an Image object to another Image that is already in the UI instead of setting the Source property of the Image to that of the current Image, you will get this error.

Without seeing your code, it will be impossible for us to work out why you got this error... from your stack trace, I'm guessing that you get this error when ShowDialog() is called, but there's not much of a clue there except that the problem is probably in that dialog or view.

Hopefully now that you understand the problem a little bit better, you may be able to fix it yourself.

Answer 2

I had a similar error because I had another (different) object interact with the WPF control before I used it. It was some old code that I needed to delete. My exeption message was similar ... The root Visual of a VisualTarget cannot have a parent. Make sure the control is only used once. In my case I put the WPF control in a Winforms ElementHost and then tried to use it in a WPF host.