Unity-Technologies/UnityCsReference · error · InvalidOperationException

Unexpected UnityEngine.Object type in Hierarchy {obj.GetType

Error message

Unexpected UnityEngine.Object type in Hierarchy {obj.GetType()}

What it means

Thrown during hierarchy drag-drop when the EntityId resolves to a UnityEngine.Object that is not a GameObject. The drop logic expects to obtain a Transform parent from a GameObject; any other Object type (e.g. a material, scriptable object, or asset) is an unexpected hierarchy entry.

Source

Thrown at Editor/Mono/GUI/TreeView/AssetOrGameObjectTreeViewDragging.cs:285

                // Require all dragged objects to be valid (since native cannot filter out invalid sub scene drags currently)
                if (SubSceneGUI.IsChildOrSameAsOtherTransform(parentForDrop, gameObject.transform))
                    return false;
            }

            // Valid drop target for current dragged objects
            return true;
        }

        Transform GetTransformParentForDrop(EntityId gameObjectOrSceneInstanceID, DropPosition dropPosition)
        {
            var obj = EditorUtility.EntityIdToObject(gameObjectOrSceneInstanceID);
            if (obj != null)
            {
                // Find transform parent from GameObject
                var go = obj as GameObject;
                if (go == null)
                    throw new InvalidOperationException("Unexpected UnityEngine.Object type in Hierarchy " + obj.GetType());

                switch (dropPosition)
                {
                    case DropPosition.Upon:
                        return go.transform;

                    case DropPosition.Below:
                    case DropPosition.Above:
                        if (go.transform.parent == null)
                        {
                            var subSceneInfo = SubSceneGUI.GetSubSceneInfo(go.scene);
                            if (subSceneInfo.isValid)
                                return subSceneInfo.transform;
                        }
                        return go.transform.parent;
                    default:
                        throw new InvalidOperationException("Unhandled enum " + dropPosition);
                }

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Verify the drop target is a GameObject before initiating a hierarchy drop.
2. Skip drop targets where EditorUtility.EntityIdToObject returns a non-GameObject and show 'invalid target' feedback.
3. Reimport/refresh assets if EntityId mapping appears stale.

Example fix

// before
var parent = GetTransformParentForDrop(id, pos); // id may map to non-GameObject

// after
var obj = EditorUtility.EntityIdToObject(id);
if (obj is GameObject go)
    parent = go.transform;
else { DragAndDrop.visualMode = DragAndDropVisualMode.Rejected; return; }

var obj = EditorUtility.EntityIdToObject(id); if (!(obj is GameObject)) { DragAndDrop.visualMode = DragAndDropVisualMode.Rejected; return; }

static bool IsHierarchyGameObject(EntityId id) => EditorUtility.EntityIdToObject(id) is GameObject;

When it happens

Trigger: Dropping onto a hierarchy node whose EntityId maps to a non-GameObject asset; a corrupted or custom hierarchy item returning an unsupported Object subtype.

Common situations: Custom hierarchy window extensions injecting non-GameObject items; stale EntityId references after asset import changes; scene state desync.

Related errors

• Unhandled enum {dropPosition}
• ApplyPrefabAddedGameObjects requires that GameObjects share
• HierarchyProperty is deprecated. Use HierarchyIterator inste
• Unexpected resultBits Span length. The expected length of re
• ScriptableBakedReflectionSystemWrapper

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/717b19ab82817dce. Report an issue: GitHub.