Unity-Technologies/UnityCsReference · error · ArgumentException

Calling apply or revert methods on an object which is not pa

Error message

Calling apply or revert methods on an object which is not part of a Prefab instance is not supported.

What it means

Thrown by ThrowExceptionIfNotValidPrefabInstanceObject when the object is a non-null GameObject/Component but is NOT part of a prefab instance (PrefabUtility.IsPartOfPrefabInstance returns false). Apply/revert operate on overrides within prefab instances, so a plain scene object or an unpacked object is invalid.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.cs:249

                    }
                }
            }

            foreach (var path in assetsToReload)
            {
                AssetDatabase.WriteImportSettingsIfDirty(path);
                AssetDatabase.ImportAsset(path, ImportAssetOptions.ForceUpdate);
            }
        }

        static void ThrowExceptionIfNotValidPrefabInstanceObject(Object prefabInstanceObject, bool isApply)
        {
            if (!(prefabInstanceObject is GameObject || prefabInstanceObject is Component))
                throw new ArgumentException("Calling apply or revert methods on an object which is not a GameObject or Component is not supported.", nameof(prefabInstanceObject));
            if (prefabInstanceObject == null)
                throw new NullReferenceException("Cannot apply or revert object. Object is null.");
            if (!PrefabUtility.IsPartOfPrefabInstance(prefabInstanceObject))
                throw new ArgumentException("Calling apply or revert methods on an object which is not part of a Prefab instance is not supported.", nameof(prefabInstanceObject));

            // We support revert operations on Prefab Assets, but not apply operations.
            if (isApply)
                ThrowExceptionIfInstanceIsPersistent(prefabInstanceObject);
        }

        static void ThrowExceptionIfAllPrefabInstanceObjectsAreInvalid(Object[] prefabInstanceObjects, bool isApply)
        {
            foreach (var obj in prefabInstanceObjects)
            {
                if (obj != null && (obj is GameObject || obj is Component) && IsPartOfPrefabInstance(obj) && !(isApply && EditorUtility.IsPersistent(obj)))
                    return;
            }

            // Throw exception if all objects are invalid
            throw new ArgumentException("Cannot apply or revert on any of the objects. Attempt with individual objects for details.", nameof(prefabInstanceObjects));
        }

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Ensure the object is part of a prefab instance: check IsPartOfPrefabInstance first.
2. If unpacked, reconnect via InstantiatePrefab or reapply to a valid instance.
3. For revert-on-asset flows use the asset path variant; for apply, operate on an instance in a scene.

Example fix

// before
PrefabUtility.ApplyPrefabOverride(unpackedGo, path);

// after
if (!PrefabUtility.IsPartOfPrefabInstance(obj))
{ Debug.LogWarning("Object is not part of a prefab instance."); return; }
PrefabUtility.ApplyPrefabOverride(obj, path);

if (!PrefabUtility.IsPartOfPrefabInstance(obj))
{ Debug.LogWarning("Object is not part of a prefab instance."); return; }

static bool IsPrefabInstanceObject(UnityEngine.Object o) => o is GameObject || o is Component && PrefabUtility.IsPartOfPrefabInstance(o);

When it happens

Trigger: Passing a regular scene GameObject with no prefab connection, an unpacked prefab, or an object whose instance link was stripped. Passing a prefab asset (which is not an 'instance').

Common situations: Operating on objects after PrefabUtility.UnpackPrefabInstance severed the link. Selecting plain scene objects in a custom apply tool. Forgetting that revert on a prefab asset is allowed but apply is not.

Related errors

• Calling apply or revert methods on an object which is not a
• Cannot apply or revert object. Object is null.
• Cannot apply or revert on any of the objects. Attempt with i
• The Prefab you want to instantiate is null.
• ApplyPrefabAddedGameObjects requires that GameObjects share

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/cfd36d9bb8b4b15a. Report an issue: GitHub.