Bug Exception when RemoveFromHierarchy

I just updated from Unity 2021.3.19f to Unity 2022.2.13.f1 and got the following error when trying to remove an element:

It just happen just there in my popup manager, the rest of the game seems fine. No idea how to debug the problem there.

Code (CSharp):

1. NullReferenceException: Object reference not set to an instance of an object
2. UnityEngine.UIElements.VisualElement.WillChangePanel (UnityEngine.UIElements.BaseVisualElementPanel destinationPanel) (at <baee2ba96d3743838f9756565b830367>:0)
3. UnityEngine.UIElements.VisualElement.SetPanel (UnityEngine.UIElements.BaseVisualElementPanel p) (at <baee2ba96d3743838f9756565b830367>:0)
4. UnityEngine.UIElements.VisualElement+Hierarchy.SetParent (UnityEngine.UIElements.VisualElement value) (at <baee2ba96d3743838f9756565b830367>:0)
5. UnityEngine.UIElements.VisualElement+Hierarchy.RemoveAt (System.Int32 index) (at <baee2ba96d3743838f9756565b830367>:0)
6. UnityEngine.UIElements.VisualElement+Hierarchy.Remove (UnityEngine.UIElements.VisualElement child) (at <baee2ba96d3743838f9756565b830367>:0)
7. UnityEngine.UIElements.VisualElement.RemoveFromHierarchy () (at <baee2ba96d3743838f9756565b830367>:0)
8. PopupManager.ClosePopup (System.Boolean easy) (at Assets/Assemblies/Core/UI/PopupManager.cs:177)

Update: Also found it when stopping playmode in unity, without my code involved:

Code (CSharp):

1. NullReferenceException: Object reference not set to an instance of an object
2. UnityEngine.UIElements.VisualElement.WillChangePanel (UnityEngine.UIElements.BaseVisualElementPanel destinationPanel) (at <baee2ba96d3743838f9756565b830367>:0)
3. UnityEngine.UIElements.VisualElement.SetPanel (UnityEngine.UIElements.BaseVisualElementPanel p) (at <baee2ba96d3743838f9756565b830367>:0)
4. UnityEngine.UIElements.VisualElement+Hierarchy.SetParent (UnityEngine.UIElements.VisualElement value) (at <baee2ba96d3743838f9756565b830367>:0)
5. UnityEngine.UIElements.VisualElement+Hierarchy.RemoveAt (System.Int32 index) (at <baee2ba96d3743838f9756565b830367>:0)
6. UnityEngine.UIElements.VisualElement+Hierarchy.Remove (UnityEngine.UIElements.VisualElement child) (at <baee2ba96d3743838f9756565b830367>:0)
7. UnityEngine.UIElements.VisualElement.RemoveFromHierarchy () (at <baee2ba96d3743838f9756565b830367>:0)
8. UnityEngine.UIElements.UIDocumentList.RemoveFromListAndFromVisualTree (UnityEngine.UIElements.UIDocument uiDocument) (at <baee2ba96d3743838f9756565b830367>:0)
9. UnityEngine.UIElements.PanelSettings.DetachUIDocument (UnityEngine.UIElements.UIDocument uiDocument) (at <baee2ba96d3743838f9756565b830367>:0)
10. UnityEngine.UIElements.UIDocument.RemoveFromHierarchy () (at <baee2ba96d3743838f9756565b830367>:0)
11. UnityEngine.UIElements.UIDocument.OnDisable () (at <baee2ba96d3743838f9756565b830367>:0)

Also when i just close the scene. Happens all the time... And afterwards getting follow up errors, i guess due to the stop of the remove. Its really a blocking issue

 

I investigated more in it and it looks like the panel got null in the willChange method. I use a lot of times the RemoveFromHirarchy method in DetachFromPanel Events with different usecases. I can't debug in that part of Unity, so my only solution is to workaround each single part...

I was able to make one of the usecases simple. This code causing the exception:

Code (CSharp):

1. var inside = new VisualElement();
2. var middle = new VisualElement();
3. var outside = new VisualElement();
4. middle.Add(inside);
5. outside.Add(middle);
6. inside.RegisterCallback<DetachFromPanelEvent>(evt => middle.RemoveFromHierarchy());
7. middle.RegisterCallback<DetachFromPanelEvent>(evt => outside.RemoveFromHierarchy());
8. rootVisualElement.Add(outside);
9. outside.RemoveFromHierarchy();

 

Anyone? I prepared already a testcase for it

 

I got this error now also in the compiled version from players, it seems my workarounds didn't cover all cases of it.

After the first Bug report was rejected and i got no clear response what they did, i invested more time and created an empty project with just that testcase in it and submitted another one. Lets see if this one is accepted...

 

Finally an answer, after 2 tries of get an accepted bug-report:

Already known but internal ticket: Closed... Like all my other reports, lots of time to debug, strip the error down in a simple case to get through and than just closed without further notice... Wasted effort to help unity to get better, never again wasting more time in that...

 

IN-38880

 

Oh, it got one step forward. Great, hope it will be fixed soon, getting this issue reported more often from the players in several places.

https://issuetracker.unity3d.com/is...ion-when-removefromhierarchy-method-is-called